Update Icons

Subdivided the new icons in 3 size categories. As requested by UX
Used the company naming scheme for uniformity and easy recognition.

Known issues:
- Top/Bottom category wasn't taken into account by UX at the time. Since
 this is a recent addition. Both the Walls and Top/Bottom will be updated.
- Cloud/Network connection icons 12px don't render correctly. Due to the
 theme-ing.
- Extruder Icons do not render correctly.

CURA-8010_new_icons

resources/qml/Widgets/CheckBox.qml

@@ -58,7 +58,7 @@ CheckBox
             height: Math.round(parent.height / 2.5)
             sourceSize.height: width
             color: !enabled ? UM.Theme.getColor("setting_control_disabled_text") : UM.Theme.getColor("setting_control_text")
-            source: UM.Theme.getIcon("check")
+            source: UM.Theme.getIcon("Check")
             opacity: control.checked ? 1 : 0
             Behavior on opacity { NumberAnimation { duration: 100; } }
         }

resources/qml/Widgets/ComboBox.qml

@@ -62,7 +62,7 @@ ComboBox
         x: control.width - width - control.rightPadding
         y: control.topPadding + Math.round((control.availableHeight - height) / 2)
 
-        source: UM.Theme.getIcon("arrow_bottom")
+        source: UM.Theme.getIcon("ChevronSingleDown")
         width: UM.Theme.getSize("standard_arrow").width
         height: UM.Theme.getSize("standard_arrow").height
         sourceSize.width: width + 5 * screenScaleFactor