Support arbitrary number of task families to be created in one process.

[HerbertJordan]

Currently, for simplicity, the number of task families supported in a single process is limited to an upper boundary:

https://github.com/allscale/allscale_api/blob/master/code/api/include/allscale/api/core/impl/reference/treeture.h#L460

This should be generalized.

[HerbertJordan]

The limit has been temporary removed for development, however this leads to a gradual built-up of small amounts of memory that will only be freed during shutdown.

The limit was removed to facilitate application development, however eventually a cleaner resource management solution needs to be integrated.