Update use of CPack components and add install targets

Update use of CPack components and add install targets

* Removed component runtime and replaced it with component "scripts",
a component for each tool, and the component group tools. This means
CPack is capable of dealing with a single tool, or with the whole
group.
* Moved gmxpreprocess library to libraries component.
* Created CPack dependencies so that shared libraries accompany
executables.
* Created non-CPack install targets for each GROMACS tool, e.g.
"make install-grompp". Shared libraries are installed with these
tools as appropriate. Using library suffices could be right here,
but that's the user's problem to solve.

Development, regression testing and bug testing is more convenient if
you can easily build and install just a subset of tools. This could
always have been done with CMake black magic, but these targets makes
lives easier. Also users can now easily install MPI or
double-precision flavours of selected tools as suitable.

Change-Id: I1053f7ff91d50169ac930f1ac5b84378d3ab2e67