Warning output missed important information

[sokra]

After upgrading the uglifyjs-webpack-plugin dependency in webpack I noticied that the warnings format changed:

• Before: single warning for an asset, After: each warning separate
• Before: info about the asset, After: information missing
• Before: note about UglifyJS, After: no info

I propose to merge warnings by module and add a not about asset and uglifyjs-webpack-plugin. Example:

WARNING in ./index.js in bundle.js (uglifyjs-webpack-plugin)
6,0: Dropping side-effect-free statement
8,0: Dropping unused function someUnUsedFunction1
9,0: Dropping unused function someUnUsedFunction2
10,0: Dropping unused function someUnUsedFunction3
11,0: Dropping unused function someUnUsedFunction4
12,0: Dropping unused function someUnUsedFunction5

WARNING in ./a.js in bundle.js (uglifyjs-webpack-plugin)
3,0: Dropping unused function someRemoteUnUsedFunction1
4,0: Dropping unused function someRemoteUnUsedFunction2
5,0: Dropping unused function someRemoteUnUsedFunction3
6,0: Dropping unused function someRemoteUnUsedFunction4
7,0: Dropping unused function someRemoteUnUsedFunction5