Added export, import and share

It is possible to export file to custom directory or share it via Gmail
or similar app. This covers Issue #12, marking the end of Phase II.
Cleaned up FileDialog UI

Ironed out bugs like unsorted directories, files showing for no reason,
code indentation, etc.
Bug fixes and refinement

Icons added to FileDialog, better sorting functions, increased read
buffer.
Resolved minor UI issue

Fixed colour bugs on some Sony devices, icon pack for different
resolution devices, simplified strings.
Fixed layouts for smaller devices
Intent filter for RCS files

Now directly open RCS files from file manager or email client to import.
Improved intent filter
Revamped Payment structures

Overhauled the payment mechanism in order to make it more flexible. This
opens doors to new options like deleting activities.
Skip check when change discarded
Ability to delete activities

Now it is possible to delete activities.
Made changes persistent