Make charts page easier to use

[kengreim]

I can see two potential experiences for charts. Both might be needed depending on what the user wants.

1. Chart "browsing" - similar to current experience, users would enter an airport and get a listing of all the charts. They could then select and chart which would open directly in the app, not in an external browser. They could hit a back button to return to the chart list.

2. "Direct" charts - user could enter an airport and chart name (e.g., "sfo sstik") and the app will automatically find the right chart and open it internally. If more than one chart is found, the user would be prompted to select the right one (e.g., "sfo 28L" might list all of the approach plates for 28L").