Issue 2747 - Added empty state for tables in options page

This review also contains the following minor changes:
- Fixed: Saving empty custom filters box produced a filter with the text ""
- Added empty states for other tables (where appropriate)
- Added placeholder to whitelist domain input field
- Used `index` in `Collection.removeItem` for selecting list element
- Properly reset items list in `Collection.clearAll` instead of overwriting its `length` attribute
- Miscellaneous whitespace corrections

[saroyanm, 2015-11-30 11:24:22]

https://codereview.adblockplus.org/29329095/diff/29329096/background.js
File background.js (right):

https://codereview.adblockplus.org/29329095/diff/29329096/background.js#newco...
background.js:180: .filter(function(filter) {return !!filter;})
nice.

https://codereview.adblockplus.org/29329095/diff/29329096/options.html
File options.html (right):

https://codereview.adblockplus.org/29329095/diff/29329096/options.html#newcod...
options.html:193: <span>Test</span>
Please change Test to "Add website", also be sure that it's translatable.

https://codereview.adblockplus.org/29329095/diff/29329096/options.js
File options.js (right):

https://codereview.adblockplus.org/29329095/diff/29329096/options.js#newcode82
options.js:82: this._setEmpty(table, null);
Doesn't it make more sense to call the _setEmpty method during object
observation ?

[Thomas Greiner, 2015-12-11 16:49:35]

https://codereview.adblockplus.org/29329095/diff/29329096/options.html
File options.html (right):

https://codereview.adblockplus.org/29329095/diff/29329096/options.html#newcod...
options.html:193: <span>Test</span>
On 2015/11/30 11:24:21, saroyanm wrote:
> Please change Test to "Add website", also be sure that it's translatable.

Done. Must've forgotten to replace the placeholder. :)

https://codereview.adblockplus.org/29329095/diff/29329096/options.js
File options.js (right):

https://codereview.adblockplus.org/29329095/diff/29329096/options.js#newcode82
options.js:82: this._setEmpty(table, null);
On 2015/11/30 11:24:21, saroyanm wrote:
> Doesn't it make more sense to call the _setEmpty method during object
> observation ?

I see your line of reasoning but I'd argue that it's the Collection's job to
keep the table's state consistent whenever items are added or removed while it
is the observer's job to try to keep other parts of the UI in sync.

Basically, we should do as much as possible within the Collection. Anything
that's table-specific (e.g. whether to use an "x" or a checkbox to add/remove
items from the collection or labelling certain items as "popular") should be
handled outside.

[saroyanm, 2015-12-17 15:51:21]

LGTM