Improved parser + Many fixes and improvments

[Arnauld]

It contains several new features:

• colors and fonts preference page
• parameters highlighting
• localized keyword support through special initial comment syntax
• complete auto-completion support even within parameter

It contains fixes for

Issue #18: Pattern variants, mainly a merge from @jarosite branch and pull requests

Complete parser rewrite:

Issue #17: Doesn't recognise steps if the scenario has a Meta: tag
Issue #14: Exception when parsing story file
Issue #11: First scenario interpreted as comment if story doesn't start with newline
Issue #10: Exception occurs while editing the story file
Issue #3: Support for localization (see special comment to set the language)
Issue #2: Basic Auto-Complete

Partially done:

Issue #4: It would be nice to have bold highlighting of narrative keywords ( 'Narrative', 'As a', 'I want to', 'In order to') in the story editor.

Due to the parser refactoring, narrative keywords are identified, one just has to give them a dedicated TextAttribute.

Incoming fixes:

Issue #9: Make Parameter Prefix Customizable
Using a special comment syntax similar to the language switch e.g.:

!-- language: fr
!-- parameter-prefix: %

[keanpantraw]

Why this is still not merged?

[literalplus]

Is this still a thing, is this something that could be merged soon-ish? Would really like to use the language support introduced in this PR.