Enable using dots and underscores in usernames

Let's enable using dots and underscores in the user names. Those 'special'
characters should only be present in the middle of usernames, so
'john.doe' is valid, '.johndoe' is invalid.
Keep original file name when importing files
Add Localization::activeLocale()

We should determine the active language dynamically.
So, let's introduce Localization::activeLocale() that should be used
instead of LANGUAGE
Translate TinyMCE

Let's translate TinyMCE if language is not English.
This requires that we have to know the TinyMCE theme in the server side,
so we build the TinyMCE options as a PHP array instead of building it as
a JavsScript array.
Add file/directory existance checks to grunt

Add functions to simply check if a file and/or a directory exists.

Example:
var c5fs = require('libraries/fs');
var isDirectory = c5fs.isDirectory(path);
var isFile = c5fs.isFile(path);
var isFileOrDirectory = c5fs.fileExists(path);
Reverting always showing installation languages in English
Merge branch 'multibyte-file-importer' of https://github.com/hissy/concrete5 into hissy-multibyte-file-importer
Merge pull request #1541 from mlocati/username-with-dots-and-underscores

Enable using dots and underscores in usernames
updating user error message
Merge pull request #1618 from mlocati/add-localization-activelanguage

Add Localization::activeLanguage()
Merge pull request #1620 from mlocati/add-useful-grunt-functions

Add file/directory existance checks to grunt
Centralize configuration of TinyMCE

Currently concrete/blocks/content/editor_config.php and
concrete/elements/editor_config.php share 99% of the code.

Let's centralize this code by adding a new TinymceHelper
Restore the width = 100% for the content block
Add languages for the concrete theme
Fix for extended languages

Some TinyMCE language file has a name with locale code (ex 'zh-cn.js').
Let's support it
content importer tweak
adding composer address template
Allow customizing date format in DateNav

See https://github.com/concrete5japan/concrete5/commit/e8e6657f854571a7dad582531b630562510b9ffd#diff-9d04cbbed56e853341a0a40f2dd30ff5R58
Merge branch 'enable-tinymce-languages' of https://github.com/mlocati/concrete5 into mlocati-enable-tinymce-languages
Update file_version.php

Fixing bug 
http://www.concrete5.org/developers/bugs/5-6-2-1/code-typos-in-concrete5_model_fileversion/