Add a MarkdownInput widget, and make use of it

Signed-off-by: Skia <skia@libskia.so>
1 job for master in 4 minutes and 47 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #1071
test

00:04:47

 
Name Stage Failure
failed
test Test There is an unknown failure, please try again
----------------------------------------------------------------------
Ran 47 tests in 72.951s

FAILED (failures=2)
Custom settings failed
Connecting signals!
Creating test database for alias 'default'...
Destroying test database for alias 'default'...
ERROR: Job failed: exit code 1