Add global search to current left nav, since it seems like a win even without making any other navigation changes. I did, however, remove pipeline and schedule/sensor search, since they are now obviated by global search.

Some other tweaks and fixes:

• Widen search dialog to 600px
• Truncate description string in search results to guard against superlong repo names
• Add a "dark" theme to the search trigger to match the current nav
• Fix choosing a result that matches the user's current location (right now this just no-ops)
• Tweak outline color of search trigger

Run Dagit with empty workspace, single-repo workspace, multi-repo workspace. Use mouse and keyboard to open search.

• Verify that dialog opens/closes with mouse and keyboard behavior
• Type querystring, verify that I can use mouse or keyboard to select options, and that keyboard scrolling through results behaves (and highlights/scrolls) correctly
• Use cmd+click to open a result in new tab, verify success
• Select a result for a page I'm already on, verify that dialog simply closes