Update README.md
Remove unused imports

Replay https://github.com/akvo/akvo-flow/commit/452fbb44d5d309bfc3f4528008a9ca5a1ba4353c
Issue #1 - Remove location update callbacks when the Activity is paused.

* To avoid memory leaks and battery draining, the location updates are
not required when the Activity is inactive. Since the activity has no
direct access to the GeoQuestionView objects and the onPause() callback
has to be propagated, a new interface for QuestionViews is provided, to
allow any subclass to perform system resource cleanup when no longer needed.

Replay https://github.com/akvo/akvo-flow/commit/25a4eb6cf84300ede4860da46a4a33443a250105
Issue #1 - Update UI after releasing the LocationManager updates

* In case we go back to the same instance of the GeoQuestionView
(i.e. navigating within the same Activity), we have to update the
message shown to the user regarding the GPS status.

Replay: https://github.com/akvo/akvo-flow/commit/90874dc0121edafb3216f6394df679e2c2712a5b
Remove all references to unimplemented android folder
Check for unsent/unexported data before creating zip files

* Prevent the creation of empty directories if no data is ready to be
sent/exported.

Replay:
https://github.com/akvo/akvo-flow/commit/cb5f863f2dbdc8d80f99c758c065ea072f3f67b0
Use boolean data type to replace "true" and "false" Strings

Convert the String property into boolean, returning true if the value
matches "true", false otherwise.

Replay:
https://github.com/akvo/akvo-flow/commit/0343e515aa3d94540ce958c87fe3ff6a4bdda4c6
Issue #2 - Implement deletion of files on the device

* Split up data deletion options into 'collected data only' and
'everything'.
* Move data deletion into a background thread (AsyncTask).
* Notify user of data deletion success/failure.
* Add helper methods to Database adapter in order to get the amount of
unsent/unexported data

Replay: https://github.com/akvo/akvo-flow/commit/5c5c0447d165a3736a20b709506694cc5758dbb4
Issue #1 - Deactivate GPS updates on survey tab change

* When a geolocation question is registered to receive updates and
another tab is pressed, the GPS updates are no longer needed.
* 'Next' button and Tab explicit click flows are now merged.
* Keep track of current Tab index.
* Leave accuracy status as is, since the location is also kept. Only
'Searching' indicator is restored when the GPS updates are removed.
Add markdown extension to README file
Issue #9 - Optimize MD5 checksum algorithm for large files

* Use a byte buffer to update the MessageDiggest in blocks of 2048 bytes.
* Move MD5 checksum utility to FileUtil helper class.
Issue #9 - Fix InputStreamReader's read() value check
Issue #2 - Delete duplicate images from DCIM directory

* To avoid some camera applications' duplicate images, whenever the
image capture intent is returned, the MediaStore provider is checked to
ensure no duplications are found (most likely in the DCIM folder). If a
duplication is found, it will be deleted from the device.
Issue #2 - Move ClearDataAsyncTask to a separate file

* Move this task to a sepatate public class.
* Use a WeakReference to the Context to allow the calling Activity
being GC if it gets finished before the AsyncTask's completion.
Issue #2 - Rephrase data deletion option for a clearer approach
Issue #2 - Rename keepSurveys flag to responsesOnly
Issue #13 - Search for lower case response headers to avoid HttpUrlConnection bug.

* Prior to Gingerbread, HttpUrlConnection converted all response
headers to lower case. This is a workaround to ensure we cover
those situations as well
Issue #12 - Remove the "Submit Data Only" option

* Force all the data to be sent together (Text Data + Images)
Issue #11 - Use the checksum of the images as fallback

* If no datetime attribute is found in the exif, compute the MD5
checksum of both images to determine if they are the same.
Issue #14 - Create a helper class to wrap formZip() response

* Define ZipFileData to hold zip file's metadata.
* Use interfaces for declarations. Classes for implementations.