Merge pull request #56 from mosteo/master

Less strict singer selection in duet TXT format

I checked all and it looks ok to me.
Use C++ compiler, not C compiler, for determining the version.
Rework findFile logic and add listFiles that can be used for scanning data files recursively, and getThemePaths for listing all theme/data folders.
Load custom fonts from theme/data folders rather than installing them (issue #40).
Revert "Windows installer: Install fonts globally to C:\Windows\Fonts."

This reverts commit 651f4958dd65131625dff0015fc952c22951f662.
Reason: Does not work.
Add missing FindFontconfig.cmake script.