[#585] Replacing imported JSON writing sources

* Replacing the imported JSON writing utilities
(https://github.com/akvo/akvo-flow/tree/develop/GAE/src/org/waterforpeople/mapping/app/util/json)
[#585] Deleting json.jar library + imported JSON source files
[#634] Handle lack of valid assignments

* Return 403 - Invalid assignment
* TODO: Use keywords instead of message?
* TODO: writeOkResponse implies a successful response. Consider alternatives
[#585] Remove unused import and new line
Merge pull request #628 from akvo/issue/585

[#585] Cleaning up JSON* classes
Merge branch 'master' into develop
[#653] Support for RAW DATA export/import on non-monitoring groups

* When building the RAW DATA report, we need to query the Survey Group
  to know if is a _Monitoring_ group
* If is a monitoring group, we need to export 2 columns, `Identifier`
  and `Display Name`, otherwise we just keep with the old process
* When importing a RAW DATA report, we need to check if the spreadsheet
  contains the 2 extra columns
* We know the fragility of business logic based on indices, instead of
  the actual content of the column, but we're not adding more
  fragility to this process, it's fragile already ;)
[#653] Code improvement

* Based on code review from @muloem
[#653] Code cleanup based on code review

* The JSON.isNull() also checks the non-existence of a key
Merge pull request #654 from akvo/issue/653

[#653] Support for RAW DATA export/import on non-monitoring groups
[#653] Fixes issue when generating reports on non monitoring group

* The RAW DATA report was generating the content (rows 1...) with some
  columns off
* The `lastCollection` property should be set to `true` only in
  monitoring groups
[#656] Use a Text property for values longer than 500 chars

* Introduce a new property `valueText` that is used to store the
  response value for large strings (more than 500 chars)
* The `setValue` and `getValue` methods check for the properties `value`
  and `valueText` for storing and reading the value
Merge pull request #657 from akvo/issue/656

[#656] Use a Text property for values longer than 500 chars
Merge branch 'master' into develop
[#656] Add support for storing large responses in SurveyalValue

* A copy of the `QuestionAnswerStore` is made on `SurveyalValue`
Merge pull request #658 from akvo/issue/656

[#656] Add support for storing large responses in SurveyalValue
Merge branch 'master' into develop
[#634] Avoid unnecessary casting

* Rely on RestResponse parameter, and its base properties
[#634] Merge branch 'develop' into issue/634

Conflicts:
	GAE/src/org/waterforpeople/mapping/app/web/SurveyedLocaleServlet.java
[#634] Add message upon error