Local observations list implemented

[tomaszmrugalski]

Here's the problem I'm trying to solve: there are many (over 4K in my case) observation directories with all sorts of artifacts from observations. Many of them are useless junk (e.g. because SDR or antenna was disconnected). This ended up with all sorts of states - useful observations with actual decoded images, useless with various failure modes (just wav file, only log complaining about SDR missing, long wav, but nothing decoded etc.).

This evolved a bit and this PR now contains the following:

• [x] list all locally saved observations and would show their status
• [x] allow deleting useless observations (and raw, wav files if image was decoded from them)
• [x] the server now returns observation id if upload was successful
• [x] the station now logs and writes the upload status to a disk locally
• [x] fixed compatibility problem after sh update to 2.0.6
• [x] submitobs called as stand-alone script now works from a virtualenv
• [x] allow deleting uploaded observations
• [x] save metadata locally, especially if postproc or upload failed

Sadly, it does not contain any new tests...

[tomaszmrugalski]

In the current form, it's not possible to determine if an observation was uploaded or upload it later. The reason is that some crucial metadata (AOS, TCA) parameters are not recorded during observation storage on local disk.

Also, not possible to implement deleting local copy of an reservation that's been uploaded.