Support analysis of coverage combining multiple transport methods

[manumoreira]

A user should be able to select many coverage algorithms.
For the time being 2 will be enough.
Each coverage can define different time ranges
The result of combining two coverage algorithms is the union of both coverage areas

[ismaelbej]

For testing purposes, I'm using a location in Kenya at these coordinates:

    :lat -2.6305773115936937, 
    :lon 40.20024979021401

Just north of Karawa where there's a strange formation next to the river

with this configuration:

• Walking for 180 minutes

• Driving for 30 minutes

• Both