[TASK] Restore Travis builds for CMS7

CMS 7 has some cleanups going on that moves legacy code into EXT:compatibility6
This change adds it to the Build env when the branch is master.
Merge pull request #688 from cedricziel/travisFix100thTime

[TASK] Restore Travis builds for CMS7
[TASK] Drop support for TYPO3 6.1

As 6.1 reached EOL, it has already been removed from travis CI.
As a consequence, new updates shouldn't get delivered to 6.1 users.

They can, however, update manually and see if it works.
[TASK] Set introduction package to correct version