refactor into modules

[wgwz]

reading through the code i saw some opportunities to refactor. let me know what you think. the main idea is that i wanted to separate the quart app setup/controllers, from the github event handling code. i feel that it's a bit easier to read when it's split up this way. i got carried away and also decided it might be helpful to create a module that contains just messages that will get sent to users.