Restart Travis builds

[madwizard]

Restart Travis-CI builds. To do this I had to:

• move SConstruct to python3. Minor changes, xrange to range and print "" to print()
• satisfy some compilers complaining about lack of includes
• disable tests... yep
• stop installing custom icons on Mac OS
• install TGUI as it's now dependency and Ubuntu doesn't seem to have it repos

[CelticMinstrel]

Some general comments on your updates:

• The contents of those strings should also be less heavily indented.
• You need file=gitrev_hpp on the subsequent 4-5 lines as well.
• Casting definitely is safer than changing the type without being sure it's safe in all cases; I'd prefer a static_cast but am not heavily attached to that.

[CelticMinstrel]

Closing since Travis is no longer in use, although if someone spots changes in this PR that are actually required in general, they are welcome to open a new PR with just those changes.