Use wagtail-markdown instead of custom code

[jeriox]

closes #44

ToDo

• fix ToC and abbr rendering
• add translation stuff to MarkdownField (Make MarkdownFields translatable torchbox/wagtail-markdown#102)
• add buttons to editor (Customise SimpleMDE options? torchbox/wagtail-markdown#64)

[jeriox]

so in theory this would be ready, but for whatever reason the CI is flaky AF on this PR. It keeps complaining that setuptools is not available in the environment although it is. In one place, upgrading setuptools and the dependency in question helped, but not in the next place

[frcroth]

Needs to be rebased, since the migrations changed

[jeriox]

@frcroth any idea why the installation of bootstrap suddenly fails with

Traceback (most recent call last):
  File "install-bootstrap.py", line 7, in <module>
    import requests
ModuleNotFoundError: No module named 'requests'

[frcroth]

@frcroth any idea why the installation of bootstrap suddenly fails with

Traceback (most recent call last):
  File "install-bootstrap.py", line 7, in <module>
    import requests
ModuleNotFoundError: No module named 'requests'

Because you moved poetry install behind the bootstrap installation

[coveralls]

Pull Request Test Coverage Report for Build 2994967157

• 35 of 36 (97.22%) changed or added relevant lines in 9 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+4.5%) to 59.951%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
myhpi/core/markdown/fields.py	3	4	75.0%

Files with Coverage Reduction	New Missed Lines	%
myhpi/tenca_django/admin.py	1	0%
myhpi/tests/settings.py	1	0%

Totals
Change from base Build 2994640743:	4.5%
Covered Lines:	738
Relevant Lines:	1231

---

💛 - Coveralls

[jeriox]

@frcroth any idea why the installation of bootstrap suddenly fails with

Traceback (most recent call last):
  File "install-bootstrap.py", line 7, in <module>
    import requests
ModuleNotFoundError: No module named 'requests'

Because you moved poetry install behind the bootstrap installation

thx! wasn't aware that it depends on stuff that we install

[jeriox]

@frcroth as your PR at wagtail-markdown ist still not reviewed, I would vote for merging this PR and therefore closing #44 while keeping #117 open and build a PR that reintroduces the buttons once the dependency is ready