added '-nosymlinks' parameter

...in order to restore windows compatibility (no 'ln -s ...' command)
fixed symlink inconsistency

...so that "nosymlinks" actually means "no symlinks at all".
The heuristic of detecting the OS is not needed then.
extracted logic from ConfluencePluginList constructor

...as the default constructor gets called implicitly by sub-classes,
which leads to errors if no internet connection is avaiable.
Reverted the import order to minimize difference from the upstream. Some changes to the explanation to -nosymlink link (it always works with -download).
Merge pull request #14 from ikedam/feature/12_nosymlinks

Some adjustment for #12
Merge pull request #13 from sjka/offline
Fixed offline capability
minimize differences from the upstream.
Merge pull request #15 from ikedam/feature/13_offline_with_nowiki

 Minimize differences from the upstream of #13 .