More robust context popup

This PR make the context popup more robust. It will be displayed even when the background services (height, reframe) are failing.

If height is failing, height will display `- [m]`
If refram is failing, the simple reframe calculation is done (adding 2 and 1 million to coordinates).

Context popup is now shown directly after clicking, without waiting for the services to response, resulting in a more snappy user interface.