Move compiler settings to its right place

Why was it in directory `impl` and in package `gnieh.blue`????
Add synctex option to compiler settings.

This piece of information is required to implement #15.
Authors may decide for each paper if the SyncTeX data must be generated
upon compilation.
Configuration may also be used to change the default value when a paper
is created.
Add API to retrieve SyncTeX data

This API implements the feature required by #15.
Authors (and only authors) may retrieve the generated SyncTeX data for
any given paper.
Write response back to the client

Not writing anything is bad, just tell the client that everything went
ok when joining/leaving.
Code cleanup.

Remove useless imports
Delete png files after compilation succeeded

If compilation of a paper succeeded, generated png pages are now
probably obsolete.
Tell client that the response is gzipped

As requested in #20, to make the browser gunzip the content itself,
setting the right header should do the trick.
I am not sure whether it is the best solution however, how do other HTTP
clients react to this? We should investigate further if this is
portable.
[imp #2] Update SynchroServer interface

Change session() function return type: instead of plain String, we now expect a
Try[String]. This allows error processing and handling at caller level.
[imp #2] Add synchronization API

New synchronization protocol uses "/papers/$paperId/sync"
Mobrite-compatible protocol uses "/papers/$paperId/q"
Unify resource names

We have no use of file extensions to access the \BlueLaTeX resources, it
is much cleaner to have uniform resource names, also for generated pdf
files and all other pdf stuffs. Same applies for the zip archive that
can be downloaded.

This work prepares for the API extension required by #18.
Add API to retrieve number of pages

Once the paper is compiled, one can access the number of pages that was
produced in the compiled version.

closes #18
Rename `File` utilities

This class has become much more general purpose than it used to be.
Rename the utility class to make it much clearer when used.
Register Synchronization API

When the synchronization module is started, the synchronization API must
be registered to make it available to clients.
Do not pack legacy mobwrite module by default

This feature is not needed anymore since we have our native scala
implementation of the new protocol
Code cleanup

Some useless brackets and bundle meta data removed.
Don't use CPS method

we are not using the CPS feature of scala-arm. The right way to acquire
some resource and return some value computed from this resource is to
use the `acquireAndGet` method.
Remove useless print
Set correct length and content type
Remove legacy parameter

The `density` parameter does not cope well with the SyncTeX feature.
Besides, below 100 (or 96 maybe) the rendered result is barely readable,
above, it is really huge. This parameter raises some other probems (see
tickets #15 and #19).

What could be useful however, is a parameter `thumbnail` that would
generate a small version of the page for an overview. But even that I am
not sure it would be useful to have...
Make persist function synchronous

It was asynchronous, which did not fulfill the interface contract.