Visuals

I have adapted the patch from issue 724 by alexghir9 following the
suggestion from Edvin
Visuals updated

Made some changes following suggestions from AlbertFree
Thanks
Comment updated

As per suggestion from Albet
Visuals

allows #visuals_available  gbv.HoldVisual gbv.HoldVisualPeepCount to be
used by the game to determine if and when a visual disease can appear
in-game
Tooltips for decrease / increase buttons in the research policy dialog
Refactored the code and added some comments
Reformatted the comment to conform the wiki guideline
Possible fix for issue #64

Ensure that neither of the messages from the advisor for numbers cured
or killed are displayed for the first of either as there is already
special messages for both these.
Finished updating the 0.30 changelog
Merge pull request #34 from MarkL1961/visuals

Use config setting to determine when Visual disease can appear
Merge pull request #40 from yyoon/research_policy_tooltips

Tooltips for decrease / increase buttons in the research policy dialog
Merge pull request #65 from MarkL1961/Issue--#64

Possible fix for issue #64
Merge pull request #69 from Lego3/finish_changelog_0.30

Finished updating the 0.30 changelog