conditionally add install target

[andy-held]

This change addresses item #504

closes #504

This changes visible behavior

The following changes are proposed:

Conditionally add an install meta target if there is a project that has an install rule.

The purpose of this change

cmake-server does not give an install target in project targets.

[andy-held]

Hm, this will not work with CMake versions prior to 3.11 because projects did not have the hasInstallRule field then, c.f. https://cmake.org/cmake/help/v3.10/manual/cmake-server.7.html

[andy-held]

This seems to have passed the tests, but I actually expect it to not work with CMake 3.10 and lower due to the missing field.

[yeganer]

This is awesome.

Looking at the response from the CMake server, individual targets also have the hasInstallRule property. One could use that to generate install rules for individual targets.
This would be very useful in a scenario where running the full install produces errors but the install of individual components (which are currently being developed) is possible.