[feat]: Build a base build image on install, have custom images 'FROM' that.

[cooperaj]

Perhaps, upon install, abstruse should build a base image containing all the things it needs to function as a build image (everything between the lines). This image should then be shown in the standard images UI as a "special" image that can be rebuilt and edited if the users want.

The "create new image" dialog should show something like

FROM abstruse_base
# The abstruse base image contains all the things we need to provide you with our feature set.

# add your commands here
apt-get install blah

In order to prevent the user accidentally breaking the image (maybe by overriding the CMD) some sanitisation checks should be in place so that when they save they can be prompted that what they're doing may break things (but not disallow those changes as they 'may' know what they're doing i.e. include the 'entry.sh' script in their own scripts)