Combine CUDA Leap-Frog, LINCS and SETTLE. I.

Combine CUDA Leap-Frog, LINCS and SETTLE. I.

This is the first step in combining constraints and integrator
into "UpdateAndConstraints" module. The initial merge does not
imply any performance optimisation or code clean-up. Hence, this
patch keeps all the temporary infrastructure that was built
around SETTLE, LINCS and Leap-Frog to allow them to function as
a separate units. In the following commits, this infrastructure
will be removed and these three implementations will be more closely
integrated. To enable, set GMX_UPDATE_CONSTRAIN_GPU environment
variable. Note, that environment variables GMX_LINCS_GPU,
GMX_SETTLE_GPU and GMX_INTEGRATE_GPU will no longer work.

Refs #2816, #2888

Change-Id: I8730aad0ecaa0230686fe89d1157b0da2f01f7bc