Allow prop and propPath to accept null and undefined as data

[evilsoft]

All the bases covered

As reported in this issue there was a problem when null or undefined is passed as the data to prop and propPath. As both of these functions take any a as data, they should not throw when passed terminal types. Instead they should map to Nothing.

This PR does just that. Also because safe was not really used anywhere except for those (and safeLift, but that is a story for another time), moved it out of core. Will deal with safeLift with another idea I have surrounding that function.

[coveralls]

Coverage remained the same at 100.0% when pulling 7e4294f on fix-prop into a149a0c on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 7e4294f on fix-prop into a149a0c on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 61e1d93 on fix-prop into a149a0c on master.

[evilsoft]