[Doc] Publish Dev documentation

[BRaimbault]

• [ ] English

[BRaimbault]

For simple customisation (not core developments), the major part of the documentation is now available:

• the readme has been updated: https://github.com/MSF-UK/MSF-Dashboard/blob/master/README.md#customize-the-dashboard-get-started
• and the documentation has been published: http://msf-uk.github.io/MSF-Dashboard/doc_getting-started/docs/dev-defined.html

For core developments, the code is fairly well documented, update would be required though and processing via JSDocs (to obtain a website similar to: https://msf-uk.github.io/MSF-Dashboard_doc/).

[heidieh]

Working on updating dev documentation for v1.1