Move escape handling to search edit

Makes more sense there
More conventional handling of text focus

- Switch focus to Treeview on arrow down (shift+tab to get back)
- select subquery (or whole text) on search edit focus
Add Ctrl+K shortcut for focusing search text
Expose clearQuery() method of search edit
Make escape work everywhere
Merge pull request #25 from christoffer/tweaks-to-search-edit

Tweaks to search edit