Merge 1.7-1 upload from unstable, bringing back switch to Qt 5

Dmitry Shachnevrequested to merge
mitya57/ttfautohint:merge-1.7-1 into master

The 1.8.1-1 upload by @vasudev was based on 1.6-1 and not on 1.7-1 upload by @myczko-guest, so the changes introduced in 1.7-1 got silently reverted.

This merge request brings back the changes from 1.7-1 upload, including switch from Qt 4 to Qt 5 (which closes bug 875211).

In my branch, I imported 1.7-1 on top on 1.6-1 and then merged it into master. You can also get debian/1.7-1 tag from my fork if you want.

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