Fix 'undefined' path elements if using multiRes without explicit setting it's basePath config value + minor improvements

Added missing checks of (optional and uninitialized) basePath attribute of config.multiRes. So default basePath/ tourConfig's basePath and multires basePath are the same if there is no explicit setting.

Extra dot in front of paths like 'path' and 'fallbackPath' are not necessary and may cause unexpected errors.

Added option to disable keyboard zooming

Update readme.md

Adding some notes about how to generate multires images ^_^ (it took me some time to figure it out hehe). 

Thanks by the way for this lib! I love it :D

Extra space not matching the replace condition on build

Hello,

the minified built version of pannellum.htm was not correct cause this space in the replace line was not replacing the corresponding line in src/pannellum.htm

        <link type="text/css" rel="Stylesheet" href="css/pannellum.css"/>