some initial work on making it easy to add a custom datasource without modifing the original source, #701, #553

Drag drop binding expression watcher was expensive, removed watcher after first eval, seems to still work

Save dropdown and search bindings and scope is now not loaded on dashboard load, small performance improvement

Removed add-panel tab from row editor, only add panels from the row menu now, do not want to ways to do the same thing

Checking for new version over https

Dashboard: tooltip fixes for flickering tooltips that sometimes do now want to show on hover, and for tooltips that get stuck after exiting modal, Closes #691

Fullscreen & edit state persisted to url is nearing completion, refactored fullscreen state management to a special dashboardViewState object, Issue #672