Allow ArgparsedCommand to have aliases

[stnevans]

As part of #244, I thought it would be useful if we could add aliases for Argparsed commands.

This pr allows us to give a list of aliases as an optional second argument to ArgparsedCommand.
I'm not totally sure if this is the best way to implement command aliases, so if anyone has a better idea feel free to suggest.
Example usage:
@pwndbg.commands.ArgparsedCommand(parser,aliases=["leakfind2"])
Example output:

pwndbg> leakfind
usage: leakfind [-h] [-p [PAGE_NAME]] [-o [MAX_OFFSET]] [-d [MAX_DEPTH]] [-s [STEP]] [--negative_offset [NEGATIVE_OFFSET]] address
leakfind: error: the following arguments are required: address
pwndbg> leakfind2
usage: leakfind [-h] [-p [PAGE_NAME]] [-o [MAX_OFFSET]] [-d [MAX_DEPTH]] [-s [STEP]] [--negative_offset [NEGATIVE_OFFSET]] address
leakfind: error: the following arguments are required: address

[disconnect3d]

This could turn into default argument trap (i.e. the [] is created only once and multiple calls to this method without passing aliases uses the the default value - the same object) but this could be easily spotted imho.

For reference: https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments