cubicweb-trackervcs #1806903 backport former 'source code' project tab [resolved]

used to be defined in forge using a custom project attribute (deleted from earlier releases)

prioritynormal
typeenhancement
done in0.6.0
load0.100
load left0.000
closed by#fc74e4d2fa94 make it working with vcsfile but without vcreview, and backport former project's source code tab. Closes #1655112 and #1806903