Update copyright date in some license files

Updated to have 2021 in copyright date ranges of licenses:
* license displayed by installer
* license for branding images

Author: delphidabbler

Src/Install/Assets/License.rtf

@@ -1,5 +1,5 @@
 All image files in the Src/Res/Img/Branding directory are copyright
-(C) 2012-2020, Peter Johnson (gravatar.com/delphidabbler).
+(C) 2012-2021, Peter Johnson (gravatar.com/delphidabbler).
 
 The files may not be copied or modified and may not be used in the distribution
 of derived programs without explicit permission of the copyright holder.