Change wording on notification emails

[kkilbey]

Description

As discussed in issue #624, we would like to improve the wording on the notification emails so that they better express why users are receiving them.

For discussion

How can we best convey the purpose of the email to the user? Maybe include a description that covers some or all of these points:

• these are recently posted events

• these are suggested events based on your professional interests

• please update your professional interests

@kathreenriel and @paulagaube have discussed changing this wording previously, so we may just need to finesse it a little.

[dshaykewich]

Per #681 suggest we remove this functionality.