Keep original filename patterns

[daun]

Currently, the plugin has output filenames hardcoded to 'assets/[name].[ext]?v=[hash]'. This PR would allow custom filename conventions by transforming the configured options instead of overwriting them. It detects the length of the hash and intelligently moves it to the query part, unless already set up correctly.

A few examples how the filename patterns are transformed:

In	Out	Notes
assets/[name]-[hash].js	assets/[name].js?v=[hash]	Moved hash to quer
assets/[name]-[hash].[ext]	assets/[name].[ext]?v=[hash]	Moved hash to query
assets/[name].[ext]	assets/[name].[ext]?v=[hash]	Added hash as query
assets/[name]-[hash].[ext]	assets/[name].[ext]?v=[hash]	Moved hash to query
assets/[name]-[hash:10].[ext]	assets/[name].[ext]?v=[hash:10]	Moved custom hash to query
assets/[name]-[hash][extname]	assets/[name][extname]?v=[hash]	Moved hash to query
assets/[name]-[hash:10][extname]	assets/[name][extname]?v=[hash:10]	Moved custom hash to query
assets/[name].js?v=[hash]	assets/[name].js?v=[hash]	No change - already in query
assets/[name].[ext]?v=[hash]	assets/[name].[ext]?v=[hash]	No change - already in query