Add good_words to project dict more efficiently

[windymilla]

Previously it saved the dictionary after reading each word from the good_words.txt. Now it reads them all, then does a single save at the end.

Fixes #1255

[windymilla]

Testing notes: You can use almost any text file as a good_words.txt file (5000 lines long is about a 10 second wait on my computer in master). Once you have created your good words file, open any other file (e.g. mytextfile.txt) in GG, run Tools->Spell Query, and in the dialog, use Add good/bad words. You can also create a bad_words.txt and load those via the same method. Each line in a good/bad words file is (always has been) treated as a good/bad "word". After running Add good/bad words you can edit mytextfile.dic and you should see all the good words listed (as Perl code), then below all the bad words.

[srjfoo]

This branch is undoubtedly faster than master, but this comment seems to imply that it's still saving after each addition? Or am I misinterpreting something?

[windymilla]

That function spelladdword is still used for adding a single word to the project dictionary - I added the word "single" to the comment, and that it saves the dictionary, to emphasise that. However, it used to be called multiple times when a good word list was added - I now add all the words to the internal structures, then save the dictionary once for that case, so don't use this function at all for that. The comment that it is "slow if used for bulk additions" is intended to alert a future developer not to use it for adding lots of words.