Update SalsaFlow custom scripts

Story-Id: SF-99
Change-Id: 6c17d50f20
prompt: Fix review issues

Change a prompt message.

Change-Id: 714269838d
Story-Id: SF-91
hooks/pre-commit: Fix review issues

Rename checkTags to salsaflowCommitsDetected.

Change-Id: 9540ac3320
Story-Id: SF-89
scripts: Improve error message

Tell the user what branch was active when the error occured.

Change-Id: d07a7daf18
Story-Id: SF-88
Fix release/story changes

These commands were buggy and mostly not working properly due to a few major
flaws in the implementation coming from not understanding git enough.

This patch makes sure the changes commands work properly. The patch is rather
scattered across the code base because the fixes and changes just implied
further changes in the code base. The end result should be, though, that the
release changes and story changes commands work properly now.

Change-Id: 048b5cc7f2
Story-Id: SF-88
reviewboard: Fix rbt version check

rbt 0.5.x is printing the version string to stdout while 0.6.x to stderr.
SalsaFlow didn't know about this change and it was always parsing stderr.
That is fixed now.

Story-Id: SF-11
Change-Id: 69b1927a68