Linux UX Improvements

[gurrgur]

The goal of this pull request is to make various user interface elements look more modern on linux platforms.

Menubar / Submenus before:

Menubar / Submenus before:

Aside from the changes that can be seen in the comparison screenshots, a border has been added to treeviews and listviews.

Summary of new libswell.colortheme properties

• listview_hilight
• listview_shadow
• treeview_hilight
• treeview_shadow
• menu_submenu_arrow_sel

[biopsin]

Tested; lookin good and clean. Supporting the merge of this..