Blackboard 2.0.0.7

This release includes some bugfixes and some improvements with switching themes:

• fixes error during opening boards when xml files were loaded in wrong order
• fixes some problems with switching themes
• adds support to eitcher choose a custom theme which is then stored permanent in the preferences or to automatically detect the theme (light or dark) based on the system settings
• adds support for gnome theme detection
• fixes striped table background colors

NOTE: in order to use all available themes you may need to delete your {HOME}/.BlackBoard/preferences.xml