Csproj and NuGet improvements

• Hints does not work for sln files: #34
• Add nuget push and delete commands: #27

Support for .net cli preview4

This release brings following features:

• .net cli preview4 support
• dotnet run command

Support of MSBuild based projects

This release brings support for MSBuild projects based on new csproj files (#26).

Usability fixes

#17 Added ability to define multiple packages sources for dotnet restore.
#14 Added ability to define multiple projects for dotnet build.
#18 Added ability to specify working directory for dotnet tool commands.
#23 Usage of dotnet tool startup time optimizations for CI environment.
#15 Improved reporting of .NET Core SDK

Add nuget package cache cleaner

Added nuget packages for build agents to remove packages in case of lack free disk space.

Update .NET CLI commands support

Project has been converted to Kotlin and updated .NET CLI commands support.

Retired DNX support

According to the breaking change in .NET Core tooling support DNX support become retired.

Toolchains configuration improvements

Added ability to customize toolchains location, reporting of toolchain path in build agent configuration parameters and set build agent steps requirements.

.NET CLI Support

Added following features:

• .NET CLI commands
• UI helpers for build steps
• Auto-discovery of build steps
• Improved detection of toolchains

Gradle build

Conveted project from Idea-based to gradle build