fixing an issue that prevented the start date data binding from changing the field in the template when changes were made programmatically to the start date observable
adding filter tab to state loading

(and cleaning up state.js a bit)
adding state representation for filtering

fromDate, toDate, and filters are all preserved within the state (URL)
params enabling users to share filter results through bookmarks, URL
exchanges, etc
Also, ensuring UpdateFilter button is only enabled when a filterable
layer is already active.
And Finally, replacing startDate with fromDate (so the app uses ‘from’
and ‘to’ rather than ‘start’ and ‘to’).
Merge remote-tracking branch 'origin/wcodp-md-staging' into wcodp-md-staging