feature: #41-group-index

This branch implements auto opening index files of a branch or project.

Right now the feature works as follows:

• Opening a repo, it searches for a README.md file, if thats not found then it checks for index.md
• Opening a directory it only checks for index.md

I tried implementing this as an index property in the project data tree, but I was having a lot of trouble with deep merge, so I made two small functions that attach to the component. We should be able to easily edit / allow users to create custom files names from here.

Let me know if you have any suggestions.