Watchface housekeeping and preparation for some kind of store

[moWerk]

As frequently discussed on matrix now, it would be desirable to have some kind of store for the watchfaces (and apps).
The whole store idea is not only unofficial-watchface related and will sure be discussed in a dedicated place.
In preparation to get the watchface related content in order i would like to start off with cleaning the current list in README.md by:

• Sort all WF alphabetically

• Update/correct those thumbnails in the square-column that have not been taken on Flatmesh background

• Make sure all watchfaces display correctly on square watches since most are developed on and for round screens.

• Discuss here wether to add few more columns to the list to display certain WF features

• Discuss which features to list at all.

• update all watchface image path and references to ../watchface-img/<wf-shortname>imagename.suffix

• change all asteroid_logo.png to asteroid-logo.svg

[beroset]

A few additional considerations:

1. It would be convenient to package each watchface as an ipk file so it could be installed with opkg
2. the licensing section of the readme is a bit unwieldy to read and to maintain
3. if we package watchfaces as ipk, the license notification should be in it
4. should we also do a check for non-square and non-round watches?