Change general-date helper format argument

[iamareebjamal]

Most of the formats passed to general-date are now standardized. There is no need to pass big repeated formats, it there are 3-4 of those. So, format argument should accept certain keywords and resolve them to formats, like {{general-date date 'dd MM YYYY HH:mm (z)'}} should be treated same as {{general-date date 'date-time-long'}}

This will also make changing specific formats easier in future.

If the passed in format is not a known keyword, it'll be treated as literal format. And format will be optional, with the most used format being the default

[divyamtayal]

working on it