LP1828840: Option to hide grid save settings button in angular grid

LP1828840: Option to hide grid save settings button in angular grid

To test:

1) Apply this commit.
2) Create an eg-grid in the Angular staff client without a persistKey
attribute (or use the one in the sandbox).
3) Compile the client and open the grid in your browser.  Open the
column picker menu.  Note that the Save button does not display.
4) Add an arbitrary value to the persistKey attribute.
5) Repeat step 3.  Note that the Save button does display.
6) Change the value of the persistKey attribute to "disabled".
7) Repeat step 3.  Note that the Save button does not display.

Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>