add size field to Category data class (#519)

Makes it possible to display the size of a category to the user

server/src/main/kotlin/suwayomi/tachidesk/manga/model/dataclass/CategoryDataClass.kt

@@ -12,5 +12,6 @@ data class CategoryDataClass(
     val order: Int,
     val name: String,
     val default: Boolean,
+    val size: Int,
     val meta: Map<String, String> = emptyMap()
 )

server/src/main/kotlin/suwayomi/tachidesk/manga/model/table/CategoryTable.kt

@@ -23,5 +23,6 @@ fun CategoryTable.toDataClass(categoryEntry: ResultRow) = CategoryDataClass(
     categoryEntry[order],
     categoryEntry[name],
     categoryEntry[isDefault],
+    Category.getCategorySize(categoryEntry[id].value),
     Category.getCategoryMetaMap(categoryEntry[id].value)
 )