Simpeg

- add projection map
- use creative commons footer in docs

Refactoring of Natural Source Electromagnetic Implementation. Includes Magnetotellurics, Tipper and ZTEM (minimally tested). From PR's 462, 423
- `NSEM` inherits from `SimPEG.EM`
- `SimPEG.MT` --> `SimPEG.EM.NSEM` : inherit all natural source EM functionality from `EM.NSEM`
- namespace has been updated to be consistent with `SimPEG.EM.FDEM`, in particular all problems follow the convention `ProblemXD_assumption` where `X` is the dimensionality of the problem
- `NSEM` receivers are now classes
- `RX.Point_impedance3D`, `RX.Point_impedance1D`, `RX.Point_tipper3D`
- `NSEM` have been renamed `Planewave_...`
- Documentation for NSEM

known issues and further development are covered in 452

DC and MT implementations included in base SimPEG

Many more Examples
Pip
Zero and Identity
Pymatsolver for Faster Builds on Travis

- Updates to fields object.
- Rename Transmitter to Source
- Sources no longer have sourceType, they should be implemented as classes
- Sources only take a RxList, everything else is a kwarg
- Rename LogicallyRectangularMesh to CurvilinearMesh
- Updates to anisotropy mapping
- Diagonal estimators
- Bug Fixes