[Toaster] all tasks

[Ravi Chintakunta]

I have pushed the "All tasks" code to ravi/all-tasks-feature branch.  This is still work in progress and I have pushed it for your review.

The push includes the all-tasks page and these enhancements to the basetable:

- Display the table column header as a link only if it is sortable
- Indicate the sort order as a up/down icon next to the column header

I have a few questions:

1. The UI design indicates filtering on Order, Executed, Outcome and Cache Attempt columns. What are the filtering options for these columns?

2. Is it correct to display the sstate_result for Cache Attempt?

3. Should the Task log be a link to the file, and if so should the log be opened in the browser or compressed and shown as a download.  

Thanks,
Ravi