frontend: Proper VM SystemTab Validation

UnitVmModel#validate() used async query to get max valid mem size and
thus caused race with submiting the Vm dialog so the memory was not
validated at all.

Added missing validation for whole SystemTab.

Removed unused AsyncDataProvider methods to get various memory-limit
related ConfigValues and corresponding (also unused) UnitVmModel fields.

Added support for TB memory size in MemorySizeParser and disabled
parsing of garbled input '12a30 MB' as longest valid prefix ('12 MB').

Removed ByteSizeValidation since it didn't validate anything. It
validated only String entities and the memory size is an
EntityModel<Integer>. All validation is performed in validateMemorySize
in conjuction with MemorySizeParser.

Change-Id: I33761ac7c5491c17fff928de13fdf16065d47e1e
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1069628
Signed-off-by: Martin Betak <mbetak@redhat.com>