Flask-admin: Merge Bootstrap4 support

[DandyDev]

@mrjoes there are multiple PRs open that add Bootstrap4 support. Bootstrap4 has been out for ages now.
I realize you're supporting flask-admin in your free time and I'm not entitled to anything. But is there a reason why you're not merging any of those PRs?

Is there any way in which I can help so we can get Bootstrap 4 support sooner? I'm willing to work on this!

[mrjoes]

I would love to merge them, but they all are unfinished and need additional work. I checked them at the end of 2019.

If someone would like to volunteer, create a single MR with all necessary changes and test it - I'll definitely merge it.

[DandyDev]

I can volunteer. But can you give me a pointer on:

• Which of the existing PRs is the most complete and should I use as basis
• What you feel is still missing from that PR.

Then I will make sure to add the relevant functionality, either by getting it from the other PRs, or by writing it myself.

[mrjoes]

This is the main WIP PR: https://github.com/flask-admin/flask-admin/pull/1879

I merged one of the outstanding PRs into it, other one can not be merged, but I think duplicates the changes from the other one anyway.

The PR needs testing: look and feel, forms functionality, inline editing, etc.

[mkschulze]

Could be checked for Bootstrap5 support now.

[TitaniumHocker]

Is there any updates?

[rkh-hash]

Any updates ?

[Seluj78]

Bootstrap 4 has been merged. You can already use it