Allow for tags with whitespaces and special characters

[digitalsignalperson]

Here's an attempt to solve https://github.com/akissinger/dodo/issues/29

I've tested

• [x] see correct [read/unread] counts for tags like/this in the tag panel
• [x] double clicking a tag in the tag panel correctly gives the search results for that tag
• [x] the tag in the search query itself is excluded from the shows tags

Not tested:

• adding/removing tags
• command bar
• probably some other things I'm unfamiliar with since I haven't fully explored all the features in dodo yet. I'm mainly using as a read-only interface for now as I get used to things.