Settings.js: extracted into coerceValue() the logic for string -> number|bool conversion
Settings.js: extracted into coerceValue() the logic for string -> number|bool conversion

This will be user in a later commit for implementing support for default values

ether/etherpad-lite,joequant/etherpad-lite,storytouch/etherpad-lite,storytouch/etherpad-lite,aptivate/etherpad-lite,aptivate/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,aptivate/etherpad-lite,joequant/etherpad-lite,ether/etherpad-lite,aptivate/etherpad-lite,joequant/etherpad-lite