MRU list in enhanced kernel picker

[sharoncxu]

Manage a list of previous connections and group them by kernel type/language for the user. All non-standard connections will be placed under the "Other" category.

User Scenario The user will first be shown a list of kernels:

After selecting one, they will be shown a list of all previously used kernels/connections:

If the user does not want to use a previous connection, they can "Add new kernel", which will insert a #!connect placeholder command into the notebook which they can enter the parameters for