Alidock

Users can add their own external mounts. They will be mounted under `/mnt` in the container. See 66.

This release fixes the impossibility to enter a container created with alidock on systems whose SSH client version does not expand `~` in paths.

It also improves automatic updates (by avoiding "update loops").

All v1.2.1 users should get the update automatically.

See 55.

First patch release after the great feedback from the [Starterkit](https://indico.cern.ch/event/752367/).

Git is more user-friendly: it uses nano by default as editor, and its interface is now colored by default.

The DNS fix (using `cloudflared`) works out of the box now, and in a completely transparent fashion: timeouts have been adjusted properly.

Software:

* Add license
* Fix some README errors
* Add a `--version` flag
* Improve the Git experience

Container:

* Improve aliBuild reference version