Keeps the OverviewTreePanel expanded and re-factors some code
Merge pull request #299 from TheTeam8s/fix-keepOverviewTreeOpen

Keeps the OverviewTreePanel expanded and re-factors some code
When no session is selected, no data will display in the overview detail panel
Makes buttons disabled after someone closes a tab so they can't click to edit/vote on/view statistics for the most recently selected session
remove merge conflicts