RFE: Add default Value to template variable

[Nicola Lunghi]

Please add the possibility to specificate a default value for a template variable
f.ex.

${project-name, none}
it highlight correctly the project names, but if you don't type any string and go to the next item, it inserts "none"

Can also be useful to have some other special_placeholders, like ${filename}, ${path}, ${parent_dir}