[#92] Delete empty Responses

* Automatically detect SurveyInstances without answers, and delete them
* close DB on onPause() callback
[#93] Delete empty Records

* Check for Records without SurveyInstances, and delete them
[#94] Force users to be logged in

* Move user check to SurveyGroupListActivity
* Note: Keeping track of User object within the RecordActivity is not
necessary anymore, as SurveyViewActivity can get the reference itself.
This approach will be implemented in the redesign branch (in the new Activity
to display Surveys)
[#95] Display Dialog with Saved Surveys

* Reuse CursorAdapter (move it to its own file)
* Display DialogFragment to select saved response, or create new
* Remove CURRENT status concept for a survey instance

Conflicts:
	app/src/main/java/org/akvo/flow/activity/RecordActivity.java
	app/src/main/java/org/akvo/flow/ui/fragment/ResponseListFragment.java
[#95] Check for saved responses in RecordActivity

* Don't show the dialog if not required
* Programmatically create the ListView (no need for layout file)
* Remove unnecessary call to bindView() in  CursorAdapter
[#95] Create the SurveyInstance upfront

* Always provide a survey instance to SurveyViewActivity
* Add RecordId Tag to responses list rows

Conflicts:
	app/src/main/java/org/akvo/flow/activity/RecordActivity.java
	app/src/main/java/org/akvo/flow/activity/SurveyViewActivity.java
[#95] Externalize Strings
[#92 & #93] Add TODO to improve Record/Response deletion

* Instead of executing a global query, provide the last Record/Response
[#32] Add style to ActionBar tabs

* Add hairline to tabs

Conflicts:
	app/src/main/res/values/styles.xml
[#32] Add stacked background to tabs