add email support about redmine_custom_workflows

[anteo]

Thank you, I'll think about it.

[go2null]

Not sure that methods should be added to the plugin. These should be defined in the user's custom workflow.

What may make sense is the ability to source other custom workflows/rb files so that a user can create a library for reuse. This could build on the #1 (saving and restoring workflows).

[anteo]

It's not possible to refer methods declared in other workflows now (validation of workflow will not pass calls to undeclared methods)
Workflows are not place for declaring helper functions. Maybe it make sense to implement a special type of workflows (e.g. "helper" workflows) which will run before all other workflows in which we can declare needed functions.
Then we can define "Mail helper" workflow and share it in online repository, which I hope implement soon.

[anteo]

Added Mailer#custom_email helper in the last (0.1.2) version.
It's available through repository for now.
Check the wiki for usage.