When a user recovers a page from browser history where placed a
marker in different map pane (visible map layer) marker was
successfully added to the map but the map center is the one
defined at Settings map properties so the marker was not visible
to the user.
Now when map_location form has valid coordinates we use them
instead of default map center settings. This will avoid the user to
have to rellocate the marker (or find the correct pane where the
marker was added) if already placed.
When using an editable map is better to load marker latitude, longitude and
map zoom from form fields so we can show the marker at latest position defined
by user when the page was restored from browser history.
To reproduce this behavior:
0. Undo this commit
1. Go to new proposal page
2. Place the proposal map marker
3. Go away to any other page
4. Restore new proposal page from browser history.
At this point you should not see the recently placed marker.
The same thing happens when editing a proposal.
If we do not do this a map could be initialized twice times or more
when restoring a page with a map causing weird UI effects and
loading some map layers also twice times or more.
Need to add a maps array to be able to store all initialized
(visible) maps so we can destroy them when needed. Notice that
we are destroying maps also when admin settings tabs changes
(only visible ones), this is again to avoid to re-initialize map more
than once when users navigate through settings tabs, another
option to the settings issue could be to detect if the map was
already initialized to skip uneeded initialization.
