react big calendar implementation

[digitaldonkey]

To advance from the bootstrap based theming first step is to add an alternative calendar display. It will be a block build in react using react-big-calendar as a base.
Additionally implement a new Rest-API providing what we need.

• basic react-big-calendar support. Load events provide a cache mechanism and evaluate how we can add all the features currently used
• Provide easily adaptable base theme support migrating color schemas to CSS variables
• Add tags (and their colors), Category Filter block, Tag Filter Block
• Provide a Datepickerpicker/beautify calendar navigation
• Provide a nice View Selector

Checkout work in progress at branch update-calendar-block.

Dev snapshot