Compile and link source in program class

[ProGTX]

No description provided.

[ProGTX]

Related: #12.

[ProGTX]

A lot needed to be done.

• A lot of changes in 063cc7e, which brought compilation to kernel class, but also broke a lot. The main issue was that breaking the build process into compile and link parts broke the queue order.
• Very important fix in 6d54e79 to address the wrong enqueue order - the kernel wasn't initialized at the proper time.
• Last touches on linking in 0bfef95.
• Mostly working at a70e28a.
• However, only id class was treated as a device reference, but range should also have been.
• Created a new superclass for both of these classes in 10912d0 -> point_ref class. This also allowed proper passing of ids and ranges to kernels.
• point_ref was mostly done (to cover the current tests) in da721ef.

A lot still needs to be done here, but for now it's mostly working.

[ProGTX]

A nice side effect of the point_ref class is that it implements a lot of the functionality needed for #2. Vector types may be migrated at some point to use it. However, the point_ref class has a huge overhead and should not be used much in user code - evidenced by the speedup gained by 1736a8d.