Added capability to view a paginated list of obstasks from admin menu.
 - Renamed task to obstask throughout.
 - Added ViewAllObservationTasksHandler() in main.py to view-obstask.
 - renamed route for LandsatOverlayRequestHandler to
'new-landsat-overlay'
 - added obstask-render.html
 - added view-obstasks.html and view-obstask.html
 - base.html has a new menu item for view-obstask (admin only)
 - ObservationTask in models.py has new pages(), taskurl() & listurl()
properties.
 - filters.py entries for obstask_url(), obstasks_url(), next() and 
 prev().
  - cache.py supports get_obstask_render(), get_obstasks_page(),
get_obstasks_keys_page(), get_obstasks_keys().

Other changes:
 bugfix sending email on new observation (host params) in main.py
Simplified the about page to mainly refer to the wordpress blog.
1. Replaced settings with OS environment variables for EE keys. Not
working yet.

.2 getPriorLandsatOverlay() uses the SimpleCloudScore algorithm from EE.
Note that this does not auto adjust as per the percentiles.
Improvements to display of
  Journal (paginated list of entries)
  Index (removed redundant info on Journals)
  User (similar to Index, needs to be tidied up)
Added 'tasks' menu item for all users to list all tasks.
TODO: just list my tasks, or some users tasks.
or Just list recent tasks.
Remove redundant list all tasks from the admin menu.
check in to syn git? no real changes