[Migrations] Added migration to Alter Education fields

This was missing from the patch.
[Entity] Education Duration -> EndDate added is_current_position field
[Listener] Made ControllerListener check if template is set
[Entity] Moved template/theme choice from GeneralSettings to BootstrapThemeBundle

The template/theme choices have been removed from the General Settings
entity. This is so that it can be refactored to the
BootstrapThemeBundle.
Said bundle will be responsible for managing the Theming/Templating for
Corvus, but can be used independently.
[Form] Removed getting theme/template folders from GeneralSettingsType

Also refactored to BootstrapThemeBundle.
[Service] Removed get theme/template choice from PortfolioInfoRepository.

This functionality is now provided by BootstrapThemeBundle
theme_manager service.
[Service] Getting theme/templateChoice from theme_manager

Updated all the references to getTemplateChoice to point to
theme_manager service instead of portfolioinforepository.
[View] Added stylesheets block to adminBase
[View] Added mainContentBlock to Frontend base
[View] Fixed no space in once of the apple-touch icons.
[View] Moved generator tag to top of frontend base
[View] Added screenreader h2 for Navigation in frontend base
[View] Changed page header to Header and fixed duplicate class attribute.
[View] Improved footer, changed alt to title attribute.
[View] Stopped including bootstrap.less as this is not needed anymore
[View] Wrapped title tag in spaceless
[View] Changed h2 to h1 in frontend index.
[View] Improved HTML structure of frontend. Fix #15
[View] Moved Boostrap design/layout.css to Core common.less
[View] Using Core common.less in assetic