Parser switching and sorting of transactions

[weiyang13]

Fixes #134

Expected behaviour:

1. In one tab (e.g. transaction), the commands for another tab (e.g. badd from budget) will not work and give an unknown command message.
2. Tab switching is done by keyboard shortcuts or clicking on the tab in the GUI. It can also be done through a command word (tx, rep, budget, analytics, loans). Regardless of how tab switching occurs, the above behaviour should hold.

Note: From above, we can immediately derive manual test cases for each mode of tab switching.

Unexpected problems encountered along the way:
In addition to what I described in #134 , I needed to define events for mouse clicking as it is not covered by the events for keyboard shortcut

Feel free to rename the command word for switching to your feature. It is stored in the respective ParserManager

Also, with this feature implemented, we can freely name the commands within our feature without worrying about conflicting with someone else. Use the ParserManager in your parser package to write the commands. However, right now the common commands (add, list, delete) as they are used by the existing Person feature, which is parsed directly by IchiFundParser

Edit: added sorting by date, then category, then description to fix #133