[Website] Simplify subscription emails

Currently thread subscription emails are quite overloaded with information. The number of links in the introduction are particularly distracting and confusing.

Here are my recommendations and rationale:

1. Remove the "Contact" link. Since it is almost always better to reply on the website instead of via private email. The contact link is especially confusing if you are the original author of the thread because you get an "access denied error" (see http://musescore.org/en/node/6173 )
2. Remove the first "Link" since a more direct link appears later in the email
3. Remove "Category" since it detracts from the title and the additional context is only marginally useful
4. Move the "Direct unsubscribe link (thread)" to the bottom section of the email where it is most expected and relabel the link "To unsubscribe from this particular thread go to" (see example below)
5. Change the format of the title and author to the more natural: "Title" by author (see example below)
6. Change the two line intro from "Your subscription on MuseScore / notifies you of new comments" to the single line "Your subscription on MuseScore notifies you of new comments on" since there is plenty of line width

Original format

| Greetings, David Bolton.
|
| Your subscription on MuseScore
| notifies you of new comments:
|
| Category: Support & bug reports
| Author: jmailman
| Contact: http://musescore.org/en/user/3288/contact
| Title: LocalManual
| Link: http://musescore.org/en/node/2687
| Direct unsubscribe link (thread):
| http://musescore.org/en/s/del/node/nid/2687/-1/6/f448b66459fa116db5620df743311bc0
| --------------------------------------------------------------------
| New comment:
| Author: lasconic
| Title: In the fix of this bug, I

In the fix of this bug, I didn't do anything for mac. The fix is windows
specific. Any mac user can confirm that Help -> Local is working ?
(It does for me on mac intel 10.5.8, MuseScore 0.9.6)

| Link: http://musescore.org/en/node/2687#comment-17301
| --------------------------------------------------------------------
| This is an automated message. Please do NOT reply to the sender address!
| To manage your subscriptions go to
| http://musescore.org/en/user/6/subscriptions 

Simplified format

| Greetings, David Bolton.
|
| Your subscription on MuseScore notifies you of new comments on
|
| "LocalManual" by jmailman
|
| --------------------------------------------------------------------
| New comment:
| Author: lasconic
| Title: In the fix of this bug, I

In the fix of this bug, I didn't do anything for mac. The fix is windows
specific. Any mac user can confirm that Help -> Local is working ?
(It does for me on mac intel 10.5.8, MuseScore 0.9.6)

| Link: http://musescore.org/en/node/2687#comment-17301
| --------------------------------------------------------------------
| This is an automated message. Please do NOT reply to the sender address!
|
| To unsubscribe from this particular thread go to
| http://musescore.org/en/s/del/node/nid/2687/-1/6/f448b66459fa116db5620df743311bc0
|
| To manage all your MuseScore subscriptions go to
| http://musescore.org/en/user/6/subscriptions