fixing bug #799
Proposed fix for #814
Proposed fix for #844
Fixed too frequent job cleanups

The ImportingManager cleans up jobs that has not been touched in 60ms.
According to comment this should be 60 minutes but was changed in
4529310237f9f862a0ad86d3b466b380bd9cb80c.
Fix when exporting to excel files

When exporting to excel, there cannot be more than 255 columns.
If there are more columns than that, we write "ERROR: TOO MANY
COLUMNS" to the 255th column. Formerly, OpenRefine reported
a 500 Server error.
Merge pull request #837 from ultraklon/modification2

fixing bug #799
Merge pull request #845 from ultraklon/modification4

Proposed fix for #814
Merge pull request #846 from ultraklon/modification5

Proposed fix for #844
Merge pull request #851 from Arcadelia/Job-cleanup-fix

Fixed too frequent job cleanups
Merge pull request #867 from abhillman/exceloutput255bugfix

Report error to user when attempting to export >255 columns, rather than generic 500 ISE
Merge pull request #9 from OpenRefine/master

Merge with master project