Add basic support for "between" verb, for date range grid filter

this seems to be complete, but we'll see in practice if i forgot something..

tailbone/static/js/tailbone.buefy.datepicker.js

@@ -14,6 +14,7 @@ const TailboneDatepicker = {
         ':value="value ? parseDate(value) : null"',
         '@input="dateChanged"',
         ':disabled="disabled"',
+        'ref="trueDatePicker"',
         '>',
         '</b-datepicker>'
     ].join(' '),
@@ -49,7 +50,11 @@ const TailboneDatepicker = {
 
         dateChanged(date) {
             this.$emit('input', this.formatDate(date))
-        }
+        },
+
+        focus() {
+            this.$refs.trueDatePicker.focus()
+        },
     }
 
 }

tailbone/static/js/tailbone.buefy.grid.js

@@ -1,4 +1,53 @@
 
+const GridFilterDateValue = {
+    template: '#grid-filter-date-value-template',
+    props: {
+        value: String,
+        dateRange: Boolean,
+    },
+    data() {
+        return {
+            startDate: null,
+            endDate: null,
+        }
+    },
+    mounted() {
+        if (this.dateRange) {
+            if (this.value.includes('|')) {
+                let values = this.value.split('|')
+                if (values.length == 2) {
+                    this.startDate = values[0]
+                    this.endDate = values[1]
+                } else {
+                    this.startDate = this.value
+                }
+            } else {
+                this.startDate = this.value
+            }
+        } else {
+            this.startDate = this.value
+        }
+    },
+    methods: {
+        focus() {
+            this.$refs.startDate.focus()
+        },
+        startDateChanged(value) {
+            if (this.dateRange) {
+                value += '|' + this.endDate
+            }
+            this.$emit('input', value)
+        },
+        endDateChanged(value) {
+            value = this.startDate + '|' + value
+            this.$emit('input', value)
+        },
+    },
+}
+
+Vue.component('grid-filter-date-value', GridFilterDateValue)
+
+
 const GridFilter = {
     template: '#grid-filter-template',
     props: {
@@ -14,6 +63,23 @@ const GridFilter = {
             })
         },
 
+        valuedVerb() {
+            /* this returns true if the filter's current verb should expose value input(s) */
+
+            // if filter has no "valueless" verbs, then all verbs should expose value inputs
+            if (!this.filter.valueless_verbs) {
+                return true
+            }
+
+            // if filter *does* have valueless verbs, check if "current" verb is valueless
+            if (this.filter.valueless_verbs.includes(this.filter.verb)) {
+                return false
+            }
+
+            // current verb is *not* valueless
+            return true
+        },
+
         focusValue: function() {
             this.$refs.valueInput.focus()
             // this.$refs.valueInput.select()