Fixes to win32 (un)installation process

Updated the style of ossec-installer.nsi so it is easier to read.

Turned on Uninstallation details same as is done for installtion
details.

Start to use SimpleSC plugin (Rainer Döpke) to handle the intial
stopping of the OSSEC agent service. The hope is this plugin can later
be used to do handle all of the necessary service configuration that
is required.

Added error checking around many of the (un)installation steps. There
is plenty of room for more error checking but hopefully this covers
some of the major problem areas.

Added logic to create the ossec.log on every installation.

Fixed cleaning up the bookmarks directory.

Start to use nsProcess plugin (Shengalts Aleksander aka Instructor) to
detect if either manage_agents.exe or win32ui.exe are running during
an uninstall. When they are running the uninstallation will fail to
remove those files and thus fails to remove the ossec-agent directory.
Merge pull request #159 from awiddersheim/fix_win32_install_uninstall

Fixes to win32 (un)installation process