blocks can specify primary category

app/blocks/math/compare.js

@@ -4,6 +4,7 @@ export default {
   name: "Compare Numbers",
   colour: 120,
   inputsInline: true,
+  primaryCategory: "Math",
   description: "Numerically compare two given values using the selected math operation.",
 
   connections: {

app/blocks/text/compare.js

@@ -4,6 +4,7 @@ export default {
   name: "Compare Text",
   colour: 180,
   inputsInline: true,
+  primaryCategory: "Logic",
   description: "Compare two chunks of text for equality, inequality, or inclusion.",
 
   connections: {

src/definitions/block_definition.js

@@ -40,7 +40,7 @@ class BlockDefinition {
 
   disabled = false
 
-  categories = []
+  primaryCategory = null
 
 
   getCategories() {
@@ -131,6 +131,7 @@ BlockDefinition.parseRawDefinition = function(rawBlockDefinition, definitionPath
   blockDef.definitionJS = rawBlockDefinition
   blockDef.type = rawBlockDefinition.type
   blockDef.name = rawBlockDefinition.name
+  blockDef.primaryCategory = rawBlockDefinition.primaryCategory
   blockDef.description = rawBlockDefinition.description
     ? niceTemplate(rawBlockDefinition.description)
     : ""