Merge Flow call functions

[jbrezmorf]

We want reduce duplicities between
common/flow_call.py and bayes_orig/flow123d_simulation.py

Functionalities of flow123d_simulation.py:call_flow(...):

• call 'env -i' to clean environment, should be optional
• calculation skipping logic (parameter 'result_files') out of call_flow
• merge logic detecting successful calculation:
  success if: zero return code and requested_files exist (optional parameter)

Proposed functions:

• 'env -i' move to 'cfg/flow_executable' list

• flow_call(workdir, executable_list, input_template, params={})
  .. corresponding to _prepare_inputs + _flow_subprocess
  (params are optional, cfg have specific dataclass)
  vraci stdout, stderr, ProcessResult

• output dir only with default name, every flow call in separate directory

• stdout, stderr without filebase ... common filename

• flow_check(stdout, stderr, ProcessResult, result_files:List(Path)=[], timeout=0)

  1. check existence of files (possibly use search_file)

• flow_call_wit_check