Add cmake support to generate ini files for external applications

[sithhell]

In order for HPX to load components which are compiled in an external project, we currently need to manually write a ini file such that the components get found by HPX startup.
A cmake macro which configures this ini file automatically would ease that step.

[hkaiser]

I'm afraid that's not possible as the ini file needs to refer to the component names as used by the component registration macros.

[hkaiser]

This is not as urgent anymore as we have added the executable prefix to the list of directories searched for components. As long as external applications follow the HPX directory structure, the corresponding external components will be found automatically.

[brycelelbach]

Is this still necessary?

[brycelelbach]

Closing this, as I don't think we need this anymore. Please reopen and assign to me if still needed.