A more complete set of files for testing

[jepegit]

We should include more cell-testing-files for testing purposes.

• Small files

1. Standard (simple) life-time test of half-cell with CC (OK)
2. Full cell test (simple) (MISSING)
3. Tests with CV steps (MISSING)
4. Tests with taper steps (MISSING)
5. Tests with GITT (MISSING)

• Big files

1. Complete test with many cycles that should be used in integration test(s) (MISSING)

In addition, we should probably include different versions of cellpy-files to check that it is possible to still load them (and convert them).

[jepegit]

Released v.0.3.0 so this has to be a minor updated (e.g. v.0.3.1)