Revert to default table sort when sort column is hidden

Fix an issue where a ToasterTable doesn't revert to the default sort when the current sort column is hidden.

To test:

1. Run Toaster and do a build.
2. Go to the all builds page. Note that the table is sorted by "Completed on" in reverse order.
3. Use "Edit columns" to switch on the "Started on" column.
4. Sort the table by the "Started on" column. Note that the "Started on" column is highlighted as the sort column.
5. Use "Edit columns" to hide the "Started on" column.
6. Check that the sort goes back to the default ("Completed on" in reverse order).

Related bug:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=9836

The following changes since commit 1826de5234aadb9aa51c83f86471cdd7e88b48cf (toaster-next):

toaster: loadconf Partially add back some of the layerSource parsing (2016-07-21 11:23:00 +0100)

are available in the git repository at:

git://git.yoctoproject.org/poky-contrib elliot/toaster/9836-revert_sorting
http://git.yoctoproject.org/cgit.cgi/poky-contrib/log/?h=elliot/toaster/9836-revert_sorting

Elliot Smith (2):
toaster: reset table to default orderby when orderby column is hidden
toaster-tests: add tests for reverting to default sort

 .../toaster/tests/browser/test_toastertable_ui.py  | 160 +++++++++++++++++++++
 bitbake/lib/toaster/toastergui/static/js/table.js  |  78 +++++++---
 2 files changed, 220 insertions(+), 18 deletions(-)
 create mode 100644 bitbake/lib/toaster/tests/browser/test_toastertable_ui.py

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2.7.4