Added multiple term search functionality (with default phrase search)

This pull-request is very similar to #5496
Change allows:
* in addition to the standard (phrase) search adds functionality to search multiple words separated by a space (multiple terms search)
* define the word (or word list) to search in the url hash tag #search. When page has been loaded, document is scrolling to the search results.
* specify the type of search (phrase or multiple term search) in the url hash tag #phrase (true or absent hash tag - default phrase search, false - multiple term search)
* specify the type of search (phrase or multiple term search) in UI (checkbox 'Phrase', by default this is checked).

![pdfjspull](https://cloud.githubusercontent.com/assets/10258064/5538374/73ff2626-8ad4-11e4-843e-870d821cf76c.png)

Examples:
find phrase 'Locking tames tamed tame':
#search=Locking%20tames%20tamed%20tame&phrase=true
or 
#search=Locking%20tames%20tamed%20tame

find multiple term search 'Locking tames tamed tame':
#search=Locking%20tames%20tamed%20tame&phrase=false

Screenshots:
![pdfjspull-phrase](https://cloud.githubusercontent.com/assets/10258064/5538444/051c58e4-8ad6-11e4-95a5-42c01f9fbd24.png)

![pdfjspull-multiple](https://cloud.githubusercontent.com/assets/10258064/5538446/0c22a3c8-8ad6-11e4-9e99-59ee68e4482c.png)


I'm not sure I completely understand your questions/concerns here!?

Regarding moving the code into `setHash`: that shouldn't be an issue as far as I can tell, so please try moving this code there instead.

> But in some cases requires to use PDF.js search toolbar despite the fact that the built-in search is also available.

Please note that there are some search related features that, for security reasons, are currently disabled in the Firefox versions of PDF.js. So for now, I personally don't see why the feature in this PR would be any different. See e.g. [viewer.js#L711-L713](https://github.com/mozilla/pdf.js/blob/master/web/viewer.js#L711-L713).

> For example, PDF.js is used in iframe as part of the third-party applications.

Please note that `supportsIntegratedFind` is *only* ever `true` in the Firefox versions of PDF.js, and only when the viewer is used standalone.
In all other versions of the viewer, and certainly when it's in an iframe, `supportsIntegratedFind === false`, so that shouldn't be an issue. See [viewer.js#L326-L337](https://github.com/mozilla/pdf.js/blob/master/web/viewer.js#L326-L337).

> It is very important for our application.

I understand that, but showing the `PDFFindBar` in the Firefox versions of PDF.js could be confusing for users given that it's normally not used there.
(The main use case for the viewer is, after all, to be the user interface of PDF.js for Firefox.)

> What the best way to do it? Maybe we can use the new hash tag #disableIntegratedFind and set supportsIntegratedFind in false, if #disableIntegratedFind = true?

Letting hash parameters enable/disable functions in PDF.js is a bad practice, which we are actively moving away from.
Given my answers above, I don't think that you actually need a way to toggle this feature, so I (currently) see no reason to add a parameter to the API either.