installation: updated missing requirements

* Added packages PyStemmer, py-editdist, feedparser, BeautifulSoup,
  BeautifulSoup4 and python-twitter to requirements.txt

* Added packages winpdb, mechanize and mock to requirements-extras.txt

* Upgraded MySQL-python to 1.2.4, and nympy to 1.7.0.

Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
WebStyle: fix legacy form values unicode issue

* Fixes bug related to converting form values from unicode to str
  for legacy applications.

Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
WebDoc: Bootstraped table of content

* Cleans table of contents and improves compatibility fix Bootstrap.
  (closes #1374)

Co-authored-by: Jiri Kuncar <jiri.kuncar@cern.ch>
WebStyle: support for absolute url in url_for
WebStyle: refactoring of legacy template rendering

* Introduces new Jinja2 `legacy_page.html` template to simplify
  rendering of legacy application interfaces using same HTML code
  arround generated body content.

Co-authored-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
WebStyle: fix for block javascript usage

* Moves javascript code to the end of the web page after all libraries
  are loaded.

* Touches WebAccess, WebSearch and WebSession templates.
WebSearch: fix for translatable strings

Reported-by: Tibor Simko <tibor.simko@cern.ch>
WebStyle: configurable placeholder for js assets

* Adds two blocks _top_assets and _bottom_assets to place js bundles at
  approprite places. (closes #1398)
WebSearch: fix division by zero in Pagination

Reported-by: Tibor Simko <tibor.simko@cern.ch>