Fixes to workspace.js

[baptmont]

The commit contains fixes to the following issues found when using the workspace screen:

• Error in files with multiple pages, where only some had columns. (fix in line 107 changed push to concat)
• Columns loaded from an existing rule were offset (fix in line 166 by removing half the width of the div to compensate for operation at line 219 and correct offset)
• By using expressions like $("#flag-size-s").val() ? true : false a rule with a value of false will be set to true. This happens since the expression simply checks if the textbox has a value and when an existing rule is loaded the value in the textbox is set to the string "false"; changed to $("#flag-size-s").val() == "true". This requires the value in the textbox to be exactly the string "true".
• If no flavor for the algorithm was selected an alert would be shown but the ajax request to '/jobs' would go through redirecting to a different page (fixed by changing alert to throw an exception and perform alert in a try-catch that covers the ajax request).