Use subtree instead of submodule for native Crawl code

[michaelbarlow7]

Stumbled across git subtrees at work:

http://blogs.atlassian.com/2013/05/alternatives-to-git-submodule-git-subtree/ https://developer.atlassian.com/blog/2015/05/the-power-of-git-subtree/

Looks like it'll be a neater solution for keeping the crawl code up-to-date, whilst keeping whatever minor changes we need to keep it working in our app. The current method of having a forked repo with a separate branch always felt messy to me.

[michaelbarlow7]

Had a go at this but ran into issues because the native crawl code itself contains dependencies as submodules, and the .gitmodules file detailing these submodules needs to be in the root directory. It'll work if I copy the .gitmodules file to the root directory and add the "android-crawl-console" prefix to all paths within that file, but that doesn't seem very robust.