Adds --noDownload option to InstallCommand

--noDownload option is useful when Magento is already stored in the
--installationFolder and should be only installed on the given database.

So the --noDownload option skips the download of Magento and uses the
one already stored in the --installationFolder.
Updates readme.rst for --noDownload option of InstallCommand
Throws database already exist error only for --noDownload option in InstallCommand
Bugfix in create database for InstallCommand
Merge pull request #243 from mmenozzi/develop

Adds --noDownload option to InstallCommand