Editor: Centralize applyColorScheme() to one function

(integrated from trunk branch change 99dd257 by Nathan Rijksen <n.rijksen@gmail.com>)
Editor: Set "isDark" attribute on scintilla indicating whether the user is using a dark or light scheme

(integrated from trunk branch change 6b5ad77 by Nathan Rijksen <n.rijksen@gmail.com>)
UI: Editor: Visually overhauled codeintel autocompletion popups to look more pleasing

Will use either a light or dark theme depending on the active color
scheme (maximize contrast)
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(integrated from trunk branch change 9f81b68 by Nathan Rijksen <n.rijksen@gmail.com>)
UI: Icons: The codintel icons have been updated to be more visually pleasing

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(integrated from trunk branch change f5beb2a by Nathan Rijksen
<n.rijksen@gmail.com>)