Implement the VivyDocument specification

See merge request !18

XXX: Still not closing floating docs on window close

UI: The property model takes into account the "ordered QJsonObjects" that are nothing more than QJsonArray with each element being a single QJsonObject

UTILS: Add a json builder object to hold some useful functionalities like create a QJsonArray that will be interpreted as an ordered QJsonObject by the property viewer

Those buttons seems to only work with the MPV view for some strange
reasons (don't hover with other views), so disable them for all. Now the
'float' operation is done by double-clicking and the close is done with
the view menu.

- Don't show the 'Open properties' action in views when it can be
  toggled by the QDockWidget's action
- Use constexpr things to group all dock features -> easy to view and
  understand now

- Disable the subobject linkage warning for gcc.
- Solves one shadowing pb
- Delete unused DataPtr

Fake vim

See merge request !19

Revert the commit because the std::function was not appy and a bad_call
was thrown when attempting to delete the unique_ptr...

Spoiler alert: ugly C++ here.

BUILD: Only place external headers in the precompiled header to avoid recompiling it every time a local header is changed

Also fix all the warnings present with clang and get ride of most of the
forward definitions when possible.

LIB: The 'Super' typedef is set in the abstract context/stream for more factorisation and less error-prone code