Submit to multiple problems at once

For some assignments, there are many parts to a single question but each file must be submitted on its own. 

This feature will automatically submit files to matching problems.

![marmoset screenie](https://cloud.githubusercontent.com/assets/1113218/4265626/238c0eae-3c58-11e4-9c76-d5658b2e67a8.png)

It seems pretty weird to limit it to these extensions, and I'd also assume you'd want `.zip` to have higher precedence (i.e. be earlier in the list) than `.c`. There will be some assignments where you need to submit a `a1p1.zip`, which contains `a1p1.c`.

At a minimum, I'd expect this list should be:

```
['.zip', '.txt', '.c', '.cc', '.cpp', '.h', '.hex', '.asm']
```

It would also be good to add whatever the extension for scheme files is by convention for CS courses.