Ark: Replace libgzplugin, liblzmaplugin ... with kfilterplugin

[Wang Hoi]

Hello, ark developers,
I've recently added lzma plugin to ark, after finished it, i found
both libgzplugin and liblzmaplugin have similar functionalities with
KXzFilter and KGzFilter (under kdelibs/kdecore/compression)..
And then i review KGzFilter and KXzFilter's code, still very similar,
although their "api" is simple, just handle one file(one in buffer and
one out buffer), no copyFiles etc...
Then i come to ask: would it be better to replace libgzplugin and
liblzmaplugin with one kfilterplugin ?