[core] From echo to p

core/templates/403.php

core/templates/404.php

core/templates/edit_categories_dialog.php

core/templates/error.php

core/templates/installation.php

core/templates/layout.base.php

core/templates/layout.guest.php

core/templates/layout.user.php

core/templates/login.php

core/templates/part.pagenavi.php

core/templates/update.php

lib/setup.php

lib/template.php

lib/templatelayout.php

settings/apps.php

settings/templates/admin.php

settings/templates/apps.php

settings/templates/help.php

settings/templates/oauth-required-apps.php

settings/templates/oauth.php