feat: add admin screens, permissions and navigation

Seven admin controllers in a "Studia BM" navigation group, guarded by
jz.bm.access_courses, jz.bm.access_schedule and jz.bm.access_materials,
with Polish and English labels. Date and time fields are checked by the
models before a save and answered as 422 on the field.

models/deadlines/columns.yaml

@@ -0,0 +1,12 @@
+columns:
+    due_at:
+        label: jz.bm::lang.deadlines.due_at
+    title:
+        label: jz.bm::lang.common.title
+        searchable: true
+    kind:
+        label: jz.bm::lang.deadlines.kind
+    course:
+        label: jz.bm::lang.common.course
+        relation: course
+        select: name

models/deadlines/fields.yaml

@@ -0,0 +1,33 @@
+fields:
+    title:
+        label: jz.bm::lang.common.title
+        type: text
+        span: left
+        required: true
+    due_at:
+        label: jz.bm::lang.deadlines.due_at
+        type: text
+        span: right
+        required: true
+        comment: jz.bm::lang.common.datetime_comment
+    kind:
+        label: jz.bm::lang.deadlines.kind
+        type: dropdown
+        span: left
+        required: true
+        options:
+            zaliczenie: jz.bm::lang.deadline_kinds.zaliczenie
+            egzamin: jz.bm::lang.deadline_kinds.egzamin
+            praca: jz.bm::lang.deadline_kinds.praca
+            organizacyjne: jz.bm::lang.deadline_kinds.organizacyjne
+            inne: jz.bm::lang.deadline_kinds.inne
+    course:
+        label: jz.bm::lang.common.course
+        type: relation
+        nameFrom: name
+        span: right
+        emptyOption: jz.bm::lang.common.none
+    description:
+        label: jz.bm::lang.common.description
+        type: textarea
+        size: small