Basic Android Toodle app + Rust JNA bindings

[grigoryk]

PR state as of 29/12/17 PST:

• skeleton android app with "list" and "new item" activities
• android logging support from Rust
• JNA interface into Rust which allows creating items from Java and registers a callback that listens for new items
• item sets are passed back to Java and are displayed as a list
• an attempt to avoid leaking memory at the interface layer

TODO:

• rebase on top of mentat store branch - no more SQL!
• expand "ItemJNA" struct to also have due_date and completion_date
• UI support for modifying these dates
• label support

[grigoryk]

@fluffyemily for the build issue, I had to add the NDK/bin directories into my PATH.

I'm not sure why, this isn't what I'd expect to have to do (why doesn't .cargo/config work?). Also, a side-effect is that doing so breaks a regular Firefox build, for me anyway (but that's easily remedied by adjusting your PATH again).

[grigoryk]

@fluffyemily check out a basic JNA integration.

[grigoryk]

This really needs a rebase on top of @fluffyemily's mentat branch ASAP before things diverge too far.