enhance asset mgmt

- invoke ico directly
- invoke ico only at shortcut creation
- remove "ConvertTo-Icon" Function file

- removed image from xaml
- added stackpanel to xaml
- added functions to create viewbox with image
- added logic to add image via code to xaml & customdialog
- changed title color for customdialog

- remove webinvokes for assets from main.ps1

TODO: convert images into bitmap base64 string & add them directly into invoke-WinUtiltaskbaritem.ps1

config/themes.json

@@ -21,7 +21,6 @@
         "TabRowHeightInPixels":   "50",
         "IconFontSize":     "14",
         "IconButtonSize":   "35",
-        "WinUtilIconSize":        "Auto",
         "SettingsIconFontSize":   "18",
         "CloseIconFontSize":      "18",