Bug 903137 - [SMS][MMS] Contextmenu prompt for email in message should display email address

https://bugzilla.mozilla.org/show_bug.cgi?id=903137

- Make all prompts consistent
- Ensures that dataset.isContact strings are only used to derive a true isContact boolean
- Renames ThreadUI.activateContact to ThreadUI.prompt
    - The function no longer serves as only a "contact" prompt
    - May prompt any type of recipient (contact, unknown, email)
    - May prompt from header, group list or message content
- Renames ThreadUI.genPrompt to ThreadUI.prompContact
    - genPrompt is meaningless
    - The function is explicitly for creating a prompt with a known contact
    - Includes the contact info lookup
- Converts promptContact arguments to an object, instead of named parameters
- Update LinkActionHandler to delegate to promptContact, instead of doing it's own duplicated lookup
- Adds tests to ensure that a something is displayed when something is provided
    - Could be any of the following:
      - DOM UL
      - Email address
      - Phone Number
      - Name
- Updates LinkActionHandler tests to use the correct new function names

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>