Added support for OneDrive shared folders.

[dwmuller]

Addresses issue #134.

This adds support for shared folders which a user has "added
to their OneDrive". Such folders appear as, effectively, symbolic
links in the user's default root folder. These changes do not
provide a way to access other OneDrive items that have been
shared with the user.

[dwmuller]

I am open to considering a larger change that would make shared items generally accessible, but it would be a much larger set of changes that would impact (at least) URI format and item selection UI. It would require devising a way to change the URI format in a way that would be conflict-free with existing URIs. In essence, "Items Shared With me" is a set of items that are accessed through an entirely different mechanism, outside the user's default root folder.

In any case, this offering confined its changes to the OneDrive storage provider. I am happy to answer any questions you might have about it.

[Kyrodan]

Wow, thanks for this PR. I will review it an hopefully merge it to the codebase soon.

[dwmuller]

Bitte! It was a matter of scratching an itch, as they say. My wife and I share a KeePass file via OneDrive. Let me know if you have any concerns at all, stylistic, architectural, functional, robustness. I have to admit that my testing was pretty minimal. I’m a professional software developer, so I expect critical and honest reviews. 😊 I was tempted to try a more comprehensive change that would provide access to all shared items, but the changes would be much more intrusive, and I decided that would not be appropriate without prior consultation.