accelerate some deep scans and safer filter for "*~" backup files

[verdy-p]

• Accelerate deep scans by factorizing multiple regexps for the same cleaner option to reduce the number of passes (especially on large filesystems or with mounted physical hard disks or network-mounted drives).
• Safer filter for "*~" backup files (exclude "hidden" filenames starting by a "."; if needed there should be a separate option), but also adds backup filenames ending with a digit before the "~" (e.g. "index.php7~", or "README2~")

[az0]

The idea is interesting, so thanks for working on it.

Please address the errors. Here is one from Travis

======================================================================
ERROR: test_DeepScan (tests.TestDeepScan.DeepScanTestCase)
Unit test for class DeepScan.  Preview real files.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/bleachbit/bleachbit/tests/TestDeepScan.py", line 81, in test_DeepScan
    for cmd in ds.scan():
  File "/home/travis/build/bleachbit/bleachbit/bleachbit/DeepScan.py", line 105, in scan
    compiled_searches = [CompiledSearch(s) for s in searches]
  File "/home/travis/build/bleachbit/bleachbit/bleachbit/DeepScan.py", line 105, in <listcomp>
    compiled_searches = [CompiledSearch(s) for s in searches]
  File "/home/travis/build/bleachbit/bleachbit/bleachbit/DeepScan.py", line 67, in __init__
    self.regex = re_compile(search.regex)
  File "/home/travis/build/bleachbit/bleachbit/bleachbit/DeepScan.py", line 65, in re_compile
    return re.compile(regex, fs_scan_re_flags) if regex else None
  File "/opt/python/3.5.10/lib/python3.5/re.py", line 224, in compile
    return _compile(pattern, flags)
  File "/opt/python/3.5.10/lib/python3.5/re.py", line 293, in _compile
    p = sre_compile.compile(pattern, flags)
  File "/opt/python/3.5.10/lib/python3.5/sre_compile.py", line 536, in compile
    p = sre_parse.parse(p, flags)
  File "/opt/python/3.5.10/lib/python3.5/sre_parse.py", line 829, in parse
    p = _parse_sub(source, pattern, 0)
  File "/opt/python/3.5.10/lib/python3.5/sre_parse.py", line 437, in _parse_sub
    itemsappend(_parse(source, state, nested + 1))
  File "/opt/python/3.5.10/lib/python3.5/sre_parse.py", line 781, in _parse
    source.tell() - start)
sre_constants.error: missing ), unterminated subpattern at position 0
======================================================================
FAIL: test_deep_scan (tests.TestWorker.WorkerTestCase)
Test for deep scan
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/bleachbit/bleachbit/tests/TestWorker.py", line 313, in test_deep_scan
    while next(worker):
  File "/home/travis/build/bleachbit/bleachbit/bleachbit/Worker.py", line 269, in run
    yield from self.run_deep_scan()
  File "/home/travis/build/bleachbit/bleachbit/bleachbit/Worker.py", line 322, in run_deep_scan
    ds = DeepScan.DeepScan(self.deepscans)
  File "/home/travis/build/bleachbit/bleachbit/tests/TestWorker.py", line 301, in __init__
    s.regex, ['^Thumbs\\.db$', '^Thumbs\\.db:encryptable$'])
AssertionError: '^Thumbs\\.db(:encryptable)?$' not found in ['^Thumbs\\.db$', '^Thumbs\\.db:encryptable$']

Full Travis build log: https://app.travis-ci.com/github/bleachbit/bleachbit/jobs/567515304#L1093