[Settings] Various UX tweaks (#2822)

* Updated the add button styles to a standard used in W10 settings

* Updated the "About this feature" text to About [Module name]

* Set larger changes to the Shortcut Guide opacity numberbox

* Re-organised the General page

* Improved width of the add button so it's inline with the corresponding listview.

* Seperated warning label from header. Re-organised general settings

* Consistent formatting of the word 'administrator'

* Typo fix

* Warning text is collapsed when the user runs the app as admin

* Removed underline of version number

* XAML fix

src/core/Microsoft.PowerToys.Settings.UI/App.xaml

@@ -13,6 +13,7 @@
                 <ResourceDictionary Source="/Styles/_Sizes.xaml" />
                 <ResourceDictionary Source="/Styles/TextBlock.xaml" />
                 <ResourceDictionary Source="/Styles/Page.xaml"/>
+                <ResourceDictionary Source="/Styles/Button.xaml"/>
             </ResourceDictionary.MergedDictionaries>
         </ResourceDictionary>
     </Application.Resources>