Added control planning document.

controlcandidates.md

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+WINDOWS
+- DateTime Picker
+- ListView for Tables
+- Progress Bar
+- either Property Sheets or Tabs for Tabs
+- either Rebar or Toolbar for Toolbars
+- Status Bar
+- Tooltip (should be a property of each control)
+- Trackbar for Sliders
+- Tree View
+- Up-Down Control for Spinners
+- maybe:
+	- swap ComboBox for ComboBoxEx (probably only if requested enough)
+	- IP Address control (iff GTK+ and Cocoa have it; maybe not necessary if we allow arbitrary target addresses?)
+	- ListView for its Icon View?
+	- something similar to Task Dialog might be useful to have as a convenience template later
+
+GTK+
+- GtkNotebook for Tabs
+- GtkProgressBar
+- GtkScale for Sliders
+- GtkSpinButton for Spinners
+- GtkStatusBar
+- GtkToolbar
+- maybe:
+	- GtkFontButton would be nice but unless ComboBoxEx provides it Windows doesn't
+		- same for GtkColorButton
+	- GtkIconView
+	- GtkSeparator (I think Windows makes this a mode of Static controls?)
+notes to self:
+- groupbox is GtkFrame
+- GtkTreeView can do tree views and Tables
+
+COCOA
+- NSOutlineView for tree views
+- NSProgressIndicator for ProgressBar
+- NSSlider for Sliders
+- NSStatusBar
+- NSStepper for Spinners
+- NSTabView for Tabs
+- NSTableView for Tables
+- NSToolbar
+- maybe:
+	- NSBrowser seems nice...???
+	- NSCollectionView for Icon View?
+	- NSColorWell is the color button
+	- NSOpenGLView for OpenGL; need to see how much OpenGL-specific stuff I need to expose
+	- NSRuleEditor/NSPredicateEditor look nice too but
+notes to self:
+- groupbox is NSBox
+- non-editable combobox is NSPopUpButton
+- editable combobox is NSCombobox
+- don't look at NSForm; though it arranges in the ideal form layout, it only allows single-line text entry fields as controls
+- NSSecureTextField does password entries
+TODO:
+- what does NSPathControl look like?