[#164] Implement 'External Source' feature

* Read flag from XML file
* Display/Hide button in free-text questions
* Delegate question response through custom intent action
* Read the response and notify question
[#164] Refactor onActivityResult() function
[#164] Cache question ID
[#186] Cluster map markers

* Add maps utils library
* Load items directly into the cluster manager
* Upgrade min version (10)
[#193] Fetch and display username

* Remove unused Bundle attributes
[#193] Clean up

* Simplify loader callbacks (no need for ID with a single loader)
[#186] Partial update of clusters
[#164]Merge branch 'develop' into issue/164-caddisfly

Conflicts:
	app/src/main/java/org/akvo/flow/activity/SurveyActivity.java
	app/src/main/res/values/strings.xml
Merge pull request #198 from akvo/issue/164-caddisfly

Code checked
[#196] Reload all surveys

* Read all survey ids before deletion
* Tweak service to take an array of IDs as parameter
[#186] Show total amount of points in the cluster
[#186] Maximize screen bounds for computed points
[#197] Update strings
Merge pull request #199 from akvo/issue/197-unnamed-point

[#197] Update strings
[#186] Handle LatLng serialization and read
[#200] Remove extra call to fragment's refresh()

* Use resume/pause callbacks to handle DB open/close
* Remove unnecessary code in list adapter
[#200] More efficient 'mRegistered' initialization

* Remove initial DB fetch
* Initialize variable with loader's result data
[#196] Clean up
[#193] Add submitter column

* Add db column, handling db upgrades in the fall-though approach
[#193] Read SurveyInstance.SUBMITTER

* If available, display submitter