PyConf compatibility with Multi Event Scheduler

This MR adds some functionality to work with the MES introduced in Allen!429 (merged).

1. aggregates in Allen work with optional inputs (a bit like the MergingTransformer), therefore _is_optional was introduced to check for that. It is used with the all_producers function with an include_optionals flag. The all_inputs function branches too often (without caching) to be able to use it in the all_producers function.

2. mask_t type inputs in Allen algorithms are control flow inputs. They will be met by mask algorithms compiling the event list to run on. Therefore they are to be excluded from the data dependency checks.

3. Add avrg_efficiency and weight as members to the algorithm, to be able to determine good orders of algorithms in the MES

4. uses_and, uses_or .. convenience methods for the compositenode

5. force_order = False means that the MES can check permutations of orders to see what works better. therefore, the check to have force_order == True when being lazy gets in the way.

Goes with Moore!810 (merged)