Rename ObservableRole variants

Also rename corresponding CSS classes and add methods to check roles.

app-proto/src/assembly.rs

@@ -112,9 +112,17 @@ impl Element {
 }
 
 pub enum ObservableRole {
-    Measure,
-    Constrain,
-    Invalid
+    Measurement,
+    Constraint(bool)
+}
+
+impl ObservableRole {
+    pub fn is_valid_constraint(&self) -> bool {
+        match self {
+            ObservableRole::Measurement => false,
+            ObservableRole::Constraint(valid) => *valid
+        }
+    }
 }
 
 #[derive(Clone)]
@@ -126,6 +134,12 @@ pub struct Observable {
     pub role: Signal<ObservableRole>
 }
 
+impl Observable {
+    fn role_is_valid_constraint_untracked(&self) -> bool {
+        self.role.with_untracked(|role| role.is_valid_constraint())
+    }
+}
+
 // the velocity is expressed in uniform coordinates
 pub struct ElementMotion<'a> {
     pub key: ElementKey,
@@ -236,7 +250,7 @@ impl Assembly {
             let mut gram_to_be = PartialMatrix::new();
             self.observables.with_untracked(|obsls| {
                 for (_, obs) in obsls {
-                    if obs.role.with_untracked(|role| matches!(role, ObservableRole::Constrain)) {
+                    if obs.role_is_valid_constraint_untracked() {
                         let subjects = obs.subjects;
                         let row = elts[subjects.0].column_index.unwrap();
                         let col = elts[subjects.1].column_index.unwrap();