.pytool/Plugin: Add a plugin LicenseCheck

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2691
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2833
Add a plugin to check license conflict for new added
files in a patch. It will report out errors when meeting
files which are not contributed under BSD-2-Clause-Patent.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

.pytool/Plugin/LicenseCheck/Readme.md

@@ -0,0 +1,17 @@
+# License Check Plugin
+
+This CiBuildPlugin scans all new added files in a package to make sure code
+is contributed under BSD-2-Clause-Patent.
+
+## Configuration
+
+The plugin can be configured to ignore certain files.
+
+``` yaml
+"LicenseCheck": {
+    "IgnoreFiles": []
+}
+```
+### IgnoreFiles
+
+OPTIONAL List of file to ignore.