Create two new fileds "Affected Branches" and "Fixedfor Branches"

Right now we have a lot of filters (searches) based in the "Affected versions" and "Fixfor versions". While that's nice it's a bit heavy to edit all those filters each time we release new Moodle versions.

Analyse the possibility and implement two new custom fields that will group those versions into well know moodle branches, surely by getting the two first integer in the versions so:

1.9.1 ==> MOODLE_19_STABLE
1.9.2 ==> MOODLE_19_STABLE
2.0.1 ==> MOODLE_20_STABLE
a.b ==> null

Ciao

PD: I'll install them in test tracker soon. Just polishing them a bit.