Add a license header template for C++ code

Specify a file that has a license header for C++ in Preferences > C++ > File Naming > License template.

"File Naming preferences"

The license file may have special placeholders enclosed in %% that are replaced when generating a new file:

%YEAR%: Year
%MONTH%: Month
%DAY%: Day of the month
%DATE%: Date
%USER%: Username
%FILENAME%: File name
%CLASS%: Class name (if applicable)
%$VARIABLE%: Contents of environment variable VARIABLE.

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