Clean up use

[mattsignorelli]

Right now, following the convention in GTPSA, use kwarg in any kind of map or vectorfield constructor tells to create the map using the same GTPSA descriptor as specified in use (could be descriptor, TPS, map, etc). Other parameters of the map (coasting beam, radiation, spin, etc) have to be explicitly specified in other kwargs if the map is not explicitly provided. For the constructor which takes in a matrix, it might be useful to have a similar use kwarg which only takes in a map and copies all these other parameters as well.

[mattsignorelli]

use is reserved only for GTPSA descriptor, it must not do anything else