Support markdown in text fields

[KasperBrandt]

Test plan

GIVEN the project editor
WHEN looking at the description fields (all fields under section 4, except the summary)
THEN the help text should indicate that Markdown is supported

GIVEN the project page
WHEN looking at the descriptions accordion on the bottom of the summary tab
OR looking at the descriptions in the 'Full report' tab
THEN the texts should be displayed according to the Markdown rules

Issue description

We got a request to support links in text fields by Juho from Plan Finland, see https://rsrsupport.reamaze.com/admin/conversations/akvorsr-support-request-number-14087-from-juho-dot-molsa-at-plan-international-dot-org.

We could easily support markdown, using this tiny JS library for example: http://simonwaldherr.github.io/micromarkdown.js/.