add Vips as CorePlugin, re #4258

app/controllers/vips/admin.php

app/controllers/vips/api.php

app/controllers/vips/config.php

app/controllers/vips/exam_mode.php

app/controllers/vips/pool.php

app/controllers/vips/sheets.php

app/controllers/vips/solutions.php

app/views/vips/admin/edit_block.php

app/views/vips/admin/edit_grades.php

app/views/vips/config/index.php

app/views/vips/config/pending_assignments.php

app/views/vips/exam_mode/index.php

app/views/vips/exercises/ClozeTask/correct.php

app/views/vips/exercises/ClozeTask/edit.php

app/views/vips/exercises/ClozeTask/print.php

app/views/vips/exercises/ClozeTask/solve.php

app/views/vips/exercises/ClozeTask/xml.php

app/views/vips/exercises/MatchingTask/correct.php

app/views/vips/exercises/MatchingTask/edit.php

app/views/vips/exercises/MatchingTask/print.php