Ignore .jfm files in Visual Studio

.jfm files have started blocking checking for .sqlproj projects in Visual Studio. .jfm files are a new file-type created by the Microsoft ESENT database engine - this is a recent improvement only in Windows 10 Anniversary update. As the SSDT .sqlproj type in Visual Studio uses this engine for .dbmdl metadata files, and this file is locked by the user, this currently blocks users from checking into Git repositories.

This fix helps mitigate this by avoiding checkin of this file type.