Big improvement of the web application, live preview of highlighting, small fixes.

Documentation:

- improvement: changed links to explicit README.md files to folders instead (better consistency and functionality)
- fix: fixed some relative links, starting from the root of the repository

Web application:

- new: tab editor implemented
- new: live preview of highlighting
- new: JSON view of Outline
- new: JSON view of Highlight
- new: JSON view of Folding
- new: tree view of AST
- new: tree view of Outline
- new: putting introspection data into a global object for easier debugging
- change: no more editor in popup
- improvement: created a Ace editor factory function
- improvement: editor has been configured for better behavior
- improvement: the stylesheet for highlighting is now taken only once, at document initialization, for better performances
- fix: active tab is now actually displayed at application load
- documentation: cleaning
- new bug: tree views don't behave properly on updates, collapse state of nodes cannot be toggled anymore (by user action at least)

Code:

- new: sets in the object shared by nodes the id of the highest dirty node after update (the one whose subgraph has been replaced)
- new: added a more comprehensive outline
- improvement: now the graph update silently fails in case of error, allowing to enter non-correct source (waiting for a more permissive parser)
- improvement: more granularity in updates, now only the source only can be updated

Outline:

- new: added a class (model) for outline nodes

OOP:

- fix: instance properties (defined with descriptors) are now created before instance initialization. This allows both pre-initialization (input processing with schema for instance) and initialization to use these properties.