Add an immediate option to the install_extensions action

[jerearista]

There are some cases where it is beneficial to ensure an extension is installed during the bootstrap process rather than waiting till the next reload as is the current implementation. I suggest a new, optional boolean attribute be added to install_extension that, when true, calls LoadExtensions.

One use for this is when an extension installs a config file which the admin wishes to edit in a following action.

[advornic]

Workaround for now is to use run_cli_commands and copy_file.