Issue #103: Handle metre parameter in Template:Height

Extract the metre parameter for Template:Height in UnitValueParser and compute length
Merge pull request #104 from ninniuz/103_height_template_meter_param

Issue #103: Handle metre parameter in Template:Height
Issue #70: Add duration template handling

About 10k articles are using Template:Duration to specify time durations (e.g. songs or albums).
Issue #70 collects some of those.

With this change Template:Duration is parsed and a time duration in seconds is generated.
Issue #70: Add test cases for Template:Duration and Template:Height

- Added a number of test cases for Template:Duration and Template:Height based on their docs
- Fixed a problem with Template:Height parsing when either ft or in params are not defined
  (as per the template docs those cases are valid hence must be supported)
Merge pull request #105 from ninniuz/70_duration_template

Issue #70: Add duration template handling
Merge remote-tracking branch 'upstream/master'