Timed write for BLE/IP

[kvaellning]

BLE implementation for timed-write characteristic support. IP is not added, since I cannot check it and have no idea the protocol works in detail.

This fixes #227

[kvaellning]

I'll updated the unit tests, so that

• test_list_accessories_and_charateristics has now the correct permissions, and also checks for "tw"
• test_put_characteristic checks for one time write with CHAR_WRITE
• test_put_characteristic_timed_write checks for correct arguments on each call

[kvaellning]

I'll added the implementation for timed write via IP also, as specified in 6.7.2.4. I would be pleased if someone could provide the test cases.