checks for input data / validator

[domeniconappo]

We need to implement preliminary checks on user data.
Function might be implemented as a tool of lisflood-utilities so that it can be launched separately from lisflood.
From lisflood, just call this tool.

First idea is:

1. read settings to know activated modules
2. in each hydrological module, a new method will be implemented (e.g. checkinputdata()) that, based on module's list of needed files, it will check for their existence.
3. Incrementally (ie. next release of this tool), there will be additional checks for validation of data (not only existence checks).
4. files existence checks are very fast and can be executed always, before of actual model run (no need to add a new flag to ask for file checks).

[domeniconappo]

Related issue
ec-jrc/lisflood-utilities#4