Monkey configuration: add program options for configuration paths

This patch solves the issue #36.

4 additional program arguments were added for specifying different
configuration files and directories:

-m, --mimes-conf-file # path to monkey.mime
-P, --plugins-conf-dir # path to plugins configuration directory
-l, --plugin-load-conf-file # path to plugins.load file
-S, --sites-conf-dir # path to sites directory

Each option has a default value.

Monkey will try to interpret the options by prepending their values
to default configuration directory. If the obtained path does not
exist, the options will be treated as absolute paths.

I tested using ./configure --prefix=path --plugdir=--path2 and
default build. I was able to load different configuration files
from custom locations with custom names, overriding the default
names which were hardcoded in Monkey.

The patch also contains an unrelated fix to:

bin/monkey --confdir # was not working, while provided by --help

Signed-off-by: Vladimir Cernov <gg.kaspersky@gmail.com>