WebComment: general comment format improvements

* Introduces the CFG_WEBCOMMENT_ENABLE_HTML_EMAILS config variable.
  When True, emails will also include HTML content.

* Introduces the body_format column for cmtRECORDCOMMENT that describes
  the format of the body of each comment ("HTML", "TEXT", etc.).

* Handles comments appropriately when storing and displaying them,
  according to their body format and desired output format. (closes #2064)

Co-Authored-By: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
Signed-off-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
1: D100 Docstring missing
4: I102 copyright year is outdated, expected 2014 but got 2011
27:1: E302 expected 2 blank lines, found 1
27: D203 Expected 1 blank line *before* class docstring, found 0
30: D400 First line should end with '.', not 'r'
37: D400 First line should end with '.', not 's'
47:1: E302 expected 2 blank lines, found 1
47: D101 Docstring missing
49: D102 Docstring missing
55:9: E303 too many blank lines (2)
81:9: E303 too many blank lines (2)
118:26: E225 missing whitespace around operator
122:26: E225 missing whitespace around operator