Improve EntityError and SectionError views

[jhorsman]

The ServerError view view, SectionError view and EnityError view (from the DXA modules project) are not completely consistent:

view	Git project	location	uses customErrors mode
ServerError.cshtml	dxa-web-application-dotnet	Site/Views/Shared/	yes; is not used when customErrors is On
SectionError.cshtml	dxa-web-application-dotnet	Site/Views/Shared/	no; always shows HTML formatted message with error details
EntityError.cshtml	dxa-modules	Areas/Core/Views/Entity/	no; always shows HTML formatted message with error details

I propose two changes to improve this.

• Move all error views to Site/Views/Shared/ in the dxa-web-application-dotnet project. This way it is clearer to implementors that DXA expects those views to exist, even when the core module does not exist. Also, the EnityError is the only view in Areas/Core/Views/Entity/ which is not registered in the CoreAreaRegistration.
• Do not render the technical error detail in the SectionError and EntityError when the customErrors mode is 'On' in the Web.config

[rpannekoek]

Internal Issue ID (for tracking purposes): CRQ-12796