[Feature] Improve message search to include body and attachment filenames

[DrunkenHusky]

As there are a lot of E-Mails in our SMTP4Dev installation, some users dersire a search functionality. I already suggested to use the "integrated" search on site functionality from the brwoser, but that seems not enough. They want to be able to search for body contet.

So this is a Feature request to integrate a Search functionality where usesrs can search for:

• Subject content
• Body content
• From, To, CC fields
• Optional: Filename of Attachement

[Opvolger]

For a project, I created this: https://github.com/Opvolger/smtp4dev/commit/5eefff04a135eebfd6eea6de7044ea5f111d933f