Increment version to v0.7.0
Updated to Nuget 2.7 and preserved the existing logic of loading default settings
Removed callbacks from IPackageInstaller and IInstallationProvider - replaced with ILog
updated tests to reflect the removed callbacks
removed callbacks from PackageAssemblyResolver and replace with ILog. Also updated tests.
upgraded tests projects to use Nuget 2.7 too. scriptcs build version should be alpha
Merge branch 'dev' of https://github.com/scriptcs/scriptcs into stuff

Conflicts:
	src/ScriptCs.Hosting/Package/NugetInstallationProvider.cs
	src/ScriptCs.Hosting/Package/PackageInstaller.cs
	test/ScriptCs.Core.Tests/PackageAssemblyResolverTests.cs
Merge pull request #451 from filipw/nuget-upgrade

Nuget.Core upgrade to 2.7, removed old callbacks