Modularity

[TolikPylypchuk]

I've decided that I need to challenge myself even more and make this app modular, so it supports loading plugins. This will probably require changing the architecture drastically.

I haven't yet thought through about what plugins should be able to do, but there are some ideas: custom themes, localization, adiitional behaviors (like additional filtering or statistics), and additional data format support. Also, import/export can be implemented through plugins.

[TolikPylypchuk]

The app will be completely rewritten as a web app, thus all opened issues are being closed.