Use correct logic with custom URL placeholder about thunder

[RohanNagar]

Also want to customize email subject. Want to start using a EmailMessage class with a builder pattern. Also want a separate configuration object within ses for message options, and want configuration to look like:

ses:
  endpoint:
  region:
  fromAddress:
  messageOptions:
    subject:
    bodyHtmlFile:
    bodyTextFile:
    urlPlaceholderString:
    successHtmlFile:

[RohanNagar]

Work started on the email branch

More experimentation on this - taking notes here for me to remember

Create class MessageOptionsConfiguration - holds the config
Create class MessageOptions - holds the values and will be provided by EmailModule based on the config, taking care of defaults and all that
VerificationResource will take in MessageOptions and use that instead of taking in individual strings.

[RohanNagar]

Thought this was done in #172, but realized that I didn't take care of the special scenarios outlined in the main post. Keeping this open until those are done.

[RohanNagar]

Being worked on in the placeholder branch.