framebuffer.run: refresh screen after test step

The commit also refactors initialization and generic functions into a
test-environment class.

Fixes #1092.
util_mmio: refer to failed tests via line number

ref #1095
util_mmio: test Mmio::Register with 64bit width

ref #1095
util_mmio: replace test_failed by error

ref #1095
mmio: fix type inaccuracy in bitset reads

We must ensure that the type in use fits the shift value that gets
applied while combining the bitset sub-values.

ref #1095
util_mmio: test bitsets with a width of 64bit

ref #1095
util_mmio: make memory dumps easier to read

fix #1095
core: re-design memory allocator (fix #1091)

* Core_mem_allocator: implement Range_allocator interface
* Core_mem_allocator: allocate with page-granularity only
* Use slab allocators in core where meaningful (e.g. dataspace objects)