Support env-variables in path of setting 'customTemplatePath'

[FreeHarry]

To support environment variables in path of setting 'customTemplatePath' would make it easier to define absolute paths on different machines/platforms.

Variables definitions are platform dependent, e.g.

• Unix/Linux => $HOME
• Windows => %HOME%
• and ~ for the user's home directory on all systems

[martimlobao]

Honestly just having the ability to parse ~ would be a huge improvement.