Scripted fields interface

[w33ble]

Adds interface to create, edit and remove scripted fields from the index pattern.

• New interface lives in settings/indices in a new tab called "Scripted Fields"
• Button to add new scripted fields
• Interface to create an edit scripted fields
  • Includes error message when using a name that matches an existing indexed field

Also adds another change to the paginated-table directive - columns can now be marked as not sortable.

This completes the second task on #1537

[spalger]

I think it'd be really helpful if there was some info about writing scripts. Maybe warnings about dangerous operations, useful "quick start" examples, and a link to the docs for different scripting languages?

## Warning
Something about scripting being potentially expensive, but
there are ways to mitigate that...

## Reference
Our examples 

## Quick Start

**append some text to a value**
   'prefix' + doc['fieldname'].value + 'postfix'

**padd values to 20 characters**
   doc['fieldname'].value.padLeft(20, ' ')

[spalger]

I think it'd make sense to use text-align rather than float on the right column. Notice how the borders don't line up in this screenshot.

[spalger]

You probably want to clear the rowScopes array too.

[spalger]

Seeing a weird behavior when choosing the result type "string"

[spalger]

I realize that this probably works fine, but an explicit check for undefined is dangerous IMO. The scripted property is boolean and should probably be treated as true or false-y, not true or undefined.

var getScripted = type === 'scripted';
return _.where(self.fields, function (field) {
  return field.scripted ? getScripted : !getScripted;
});

[spalger]

👍