Twirl warned "Tag '@Author' is not recognised".

* Upgrade sbt from 0.13.0 to 0.13.5.
* Upgrade jsmessages from 1.6.1 to 1.6.2.
* Downgrade play-2-mail from 1.0.0 to 0.9.1.
* Split project/Build.scala into build.sbt and
  project/BuildConfig.scala.
* Introduce sbt-less.
* Introduce sbt-twirl, the new template engine for PlayFramework, and
  fix compile errors caused by it.
    * Import scala.collection.JavaConversions._ for conversion between
      Java and Scala collections.
    * Import java.lang_ and java.util._ to use java types.
    * Use implicitJavaLang imported from play.core.j.PlayMagicForJava._
      instead of lang.
    * Use requestHeader imported from play.core.j.PlayMagicForJava._
      instead of request.
    * Specify play.data.Form in full qualified name to avoid conflict
      with play.api.data.Form.
    * Fix the other template errors.
* Etc
    * Use Result instead of deprecated SimpleResult.
    * Use java.nio.file.NotDirectoryException instead of
      scalax.file.NotDirectoryException.
    * Update README to say use "acvitator" command instead of "play".
    * Add methods to PlayServlet to support Servlet 3.1

IMPORTANT NOTE: You should modify the version of h2database on which
Play depends from 1.3.175 to 1.3.176 in
~/.ivy2/cache/com.typesafe.play/play-jdbc_2.10/ivy-2.3.6.xml as follows:

        

to avoid org.h2.jdbc.JdbcSQLException because of the bug that h2database
1.3.175 cannot create or alter sequence.

 fix issue 1737, 1733, 1712
 add due date validation

- Disable label form and show "Manage Label" text
  on search form at issue list if no label exists.
- issue.View.js has rewritted with new coding convention.
- Separate pjax-filter links into partial template file.
- Set issue-info wrap affixed

- Separate LabelEditor into independent page.
- Fix label id attr `data-labelId` to `data-label-id` on relative code.
- Fix label category on view to fit new model.

* Requirements:

There is VOC to want to shows and hides menus on projects.

* Solutions:

When creating projects and change project settings, users can configure menu settings to show or hides.

Menus which can be configured are `Code`, `Issue`, `Pull Request`, `Review`, `Milestone` and `Board`.

After creating projects, only `Project Manager` can configure menu settings.

Private-issue: 601

- all editor has same data attribute that is "data-editor-mode" then wrong selection to editor of commnet.

- change selector syntax for textarea
- add data attribute for javascript selector on textarea : data-editro-mode="body"
- fix javascript error for validation at milestone

  Also, it fix mention bug when modifying comment

Cause:
About `jquery.firefox.keyfix.js`, We do not know licenses and do not have any agreements to use `it`.
Also, `this` has many unnecessary codes.

Solution:
Deletes `jquery.firefox.keyfix.js`.
Writes new codes such as `this`.

Private-issue:1450

from pull request 926

* From now, member of a group can be an assignee of the issue of the protected project

Cause:
So many files does not have copyright.

Solution:
The copyright is added to files that do not include it.