Bump version to 2.4.0 & change of naming convention

Following integration of Crashlystics (See MUZIMA-624 and MUZIMA-681), the app automatically generates crash reports and sends notifications to the project team. A notification usually includes the application version where the crash happened. Currently, it is not possible to differentiate between crash reports submitted from the application versions in production and those under development (in debugging mode), which might be important for prioritization. There is a need to update the versioning convention to enable the identification of crash reports coming from apps in production mode.

The suggested convention will be as follows:

• The versions under development should have a suffix 'SNAPSHOT'.
• Before generating a release version, the suffix will be dropped. This way, any crash report can be easily categorization.