unsqfs: Renamed variables in uncompress_table()

Prefixed them with "c" (compressed) and "u" (uncompressed) like I did
in other functions as well.
unsqfs: Added trace prints to mark the different steps in opk_sqfs_open()

This way it is easier to see which parts are causing how much I/O.
unsqfs: Fixed type for inode address

The full inode address is 48-bit: 32-bit offset for block start and
16-bit offset for inode within the block.

Bug was introduced in commit 0490960b.
unsqfs: Renamed "inode number" to "inode address"

The term "number" suggests it identifies an inode by enumerating them,
which is not the case: it contains two offsets instead, so it is more
like an address.
unsqfs: Combined metadata storage into a struct

New struct metadata_table contains the hash table and a pointer to
the decompressed data.
opkinfo: Print recognized metadata key/value pairs