Improvements to contact, participant and mailing reports

We have customised the 'event participant list' to provide some additional useful fields. I've created a PR in case people think these would be useful to add to the core product. We find the 'registered by ID' field to be particularly useful.

Edit: Did some tidying and also merged in some changes that we thought would be useful for the mailing reports.

Summary of changes

Participant report

• Add supplemental address 1 & 2 (useful since street address, city, etc. is already there)
• Add 'Registered by participant ID' (allows for reports to in/exclude 'guests', or only show guests of a certain registrant)

Contact summary

• Use existing 'getBasicContactFields' function, rather than re-defining all the fields (code tidy)
• Add 'modified date' field and filter

Contribution summary

• Code comment tidy

Mailings

• Remove unused properties, code and comment tidy
• Add more fields and filters related to 'bounces' to the bounce report
• Add custom field support to the mailing detail report