Extend task specification and editor for setting limits and category

[effa]

• limits: action blocks, energy/shots
• categories: from a fixed set of categories specified in core (with a localization label)

Notes:

• Each category will have a defined toolbox of blocks, so there is no need to specify available blocks for each task separately.
• If the limits are not specified, they could be automatically computed from the solution.

[effa]

Done. Current task format specification: https://github.com/adaptive-learning/flocs-visual-components/blob/master/docs/tasks.md