PSR-2
Indentation fixes
Show error and inhibit installation of invalid new themes
Check page_theme.php and improve theme name/description handling

- Let's check that page_theme.php defines correct class name, namespace and inheritance
- Let's introduce two new methods: getThemeName and getThemeDescription
Handle packaged themes
Merge branch 'get-theme-info-via-methods' of https://github.com/mlocati/concrete5-5.7.0 into mlocati-get-theme-info-via-methods
Fixing typo that was leading to this not installing