Bug 967440 - Remove some reflows on the keypad

- Uses shared FontSizeUtils to compute the new sizes
- Splits the font size changes and baseline into two different functions
- Removes fake nodes from previous algorithm
- call_screen.js use the single-line class rather than a test that could change
- calls_handler.js and handled_call.js now have the responsability to call ensureFixedBaseline when necessary (aka when they are displaying a known contact)
- In calls_handler.js scenario is always a second incoming call, the first one is handled by handled_call.js
- utils_test.js has been cleaned and moved to jshint
If you factor out the spy calls as I suggested in https://github.com/mozilla-b2g/gaia/pull/22219/files#discussion_r15487161, you could reset the call count here instead.