Main Menu: change Edit tab

[MartinKarim]

Description of Issue	Possible Solution	Warnings
Rank feature rated as unimportant in a user survey	Remove Rank from main menu	-
complex editing functions should be tools; sending as email does not edit anything	move Send as email and Replace string to Tools tab	see prototype in #4672
Set/clear/rename/append fields applies to whole library; item name is too long;	move to Library tab; rename to manage field names&content	see prototype in #4670
-	-	other changes can be found in issues #4665 , #4666 , #4667

[AEgit]

As long as the Rank feature is available when right-clicking an entry, I don't mind it being removed from the Main Menu. The Rank feature itself, however, absolutely needs to be remain part of JabRef, since it replaced the old marking scheme of entries using colours (which, to be honest, I still prefer). I guess this is of minor importance for people with small databases, but for someone with thousands of entries (currently >17,000 entries), the Rank feature is really useful.