Prevent blank keywords from overwriting default

When using the META_DEFAULT_KEYWORDS setting, defaults would be overwritten by a TitleMeta object with a blank keyword list.  The end result being that a user could never go back to using default keywords if they blanked out the field.
Default to page title from admin

Default page title should come from `page.get_page_title`, not `page.get_title` as djangocms page title hint says "Overwrites what is displayed at the top of your browser or in bookmarks".
README typo on pip install command
Merge pull request #6 from granteagon/develop

Prevent blank keywords from overwriting default