Gives several warnings instead of limiting input

[jorgegil]

Currently the tool gives a warning if the user tries to run an analysis and some of the input parameters are inadequate:

• CRS is not projected
• no distance values have been selected
• no network or origin layer selected

Load only layers with a projected CRS, leave message if none available. Maybe tool should lock the run button if not all requirements are met.

[jorgegil]

Fixed for network and origin. Leave messages for the rest.