Added basic pointer type support

[brkzlr]

GDB_Engine.py now has read_pointer function which can read a PointerType class containing a base_address and an offsets list. Calling this function will return the final pointed address after traversing the pointer (together with it's offsets, if it has any).

For now this PR doesn't contain offsets support in the GUI as it's a tricky feature to implement right now and have it's design similar to CE in the same time.

This is how the Add Address Dialog will look like now:

[jaredballou]

Do you have an example of the pointer offsets list, or a way I could create one via editing the PCT file or even just hard-coding one to test? I'm willing to take a crack at the GUI updates, but I want to make sure I'm understanding the proper way to encode the struct fields into the pointer type.

[korcankaraokcu]

Thanks for the contribution, very neat feature!