(core) Mappings improvements

Summary:
- Adding new icon for calendar view (the old one by just bigger)
- When there are no columns to map the select box is grayed out
- Optional mappings can be cleared now

Test Plan: Added

Reviewers: JakubSerafin

Reviewed By: JakubSerafin

Subscribers: JakubSerafin

Differential Revision: https://phab.getgrist.com/D4066

app/client/ui2018/IconList.ts

@@ -4,6 +4,7 @@ export type IconName = "ChartArea" |
   "ChartKaplan" |
   "ChartLine" |
   "ChartPie" |
+  "TypeCalendar" |
   "TypeCard" |
   "TypeCardList" |
   "TypeCell" |
@@ -152,6 +153,7 @@ export const IconList: IconName[] = ["ChartArea",
   "ChartKaplan",
   "ChartLine",
   "ChartPie",
+  "TypeCalendar",
   "TypeCard",
   "TypeCardList",
   "TypeCell",

app/client/ui2018/menus.ts

@@ -534,22 +534,25 @@ export const cssOptionRowIcon = styled(icon, `
   }
 `);
 
-const cssOptionLabel = styled('div', `
+export const cssOptionLabel = styled('div', `
   white-space: nowrap;
   overflow: hidden;
   text-overflow: ellipsis;
+  --grist-option-label-color: ${theme.menuItemFg};
+  --grist-option-label-color-sel: ${theme.menuItemSelectedFg};
+  --grist-option-label-color-disabled: ${theme.menuItemDisabledFg};
 
   .${weasel.cssMenuItem.className} & {
-    color: ${theme.menuItemFg};
+    color: var(--grist-option-label-color);
   }
 
   .${weasel.cssMenuItem.className}-sel & {
-    color: ${theme.menuItemSelectedFg};
+    color: var(--grist-option-label-color-sel);
     background-color: ${theme.menuItemSelectedBg};
   }
 
   .${weasel.cssMenuItem.className}.disabled & {
-    color: ${theme.menuItemDisabledFg};
+    color: var(--grist-option-label-color-disabled);
   }
 `);