saturate: fix possible division by 0
SaturateImage: fix: had two 'image' members, one inherited, one nullptr, which caused a crash

In particular: in "<tag><tag></tag>x</tag>" the x is now in_tag.
This fixes the rest of #20.

Also added is_in_tag function that returns a bool instead of the tag position.

This way we don't rely on rethrowing exceptions. This method has proven to work well in other projects.

fixed nullptr exception when opening a stylesheet without a game twice, the solution is to re-load when loading/validating fails the first time

Fix #25: Program throws exception when clicking on the 'stylesheet' list if there are no stylesheets.

Fixes #33

trim filenames, apparently writing a file "some card " is not possible on windows, it drops the trailing space.

This 'fixes' #18 by just removing the option to export .gif files

correct scope handling for closures, this was broken after the change to not make calls open a scope.

This means we no longer need 8 different functions for different numbers of arguments, and non-const references can now also be passed to constructors without problems.

Semi-fix bug #6 (does not work if the zipfile was loaded from a directory)