Dropping the development branch and renaming master to main

[marcelluethi]

When we started development of scalismo and scalismo-ui, we decided to follow the git-flow branching model. The main feature is to have a separate development branch.

I would argue that at this point, this model is over-complicated and no longer needed. Instead I would propose to base development on the master branch. Furthermore, I propose to rename master to main, as this is the new standard everywhere.

@Andreas-Forster You were also involved from the beginning. Do you see any reasons to keep the development branch?

[Andreas-Forster]

As it is currently evolving, I do not see any reason not to change it. Currently, it really seems to better fit our needs.

[madsendennis]

This issue already seems to be semi-implemented.
master has already been renamed to main.
Still to be done:

• Remove develop branch
• Update workflow to trigger on main instead of master and not on develop.

Anything else missing and preventing this issue from being closed?