Cleanup imports

[dlangBugzillaToGithub]

turkeyman reported this on 2014-12-30T01:24:03Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=13913

Description

C# has a tool to sort imports, and also remove imports with no referenced symbols. I think we need this is VisualD too.

Import lists are often tedious to manage, and most Visual Studio users are accustomed to the C# experience here. It's also time consuming to identify and remove redundant imports.

User experience should probably match C#.