Add new logger types; Implement LoggerManager as an EventEmmiter; Filter logs by level; Improve log layout

Only require smtp host to be present. And include username and password if they are provided.

No need to reload server for SMTP settings to take effect;
Closes #1246
Checks SMTP Settings in #1492

Add the ability to set the default language for new users.
Admin can set server default language in admin/General section.

Setting allows admin to modify Meteor.loginTokenExpires from default 90 days to something else.
Server restart is required for this setting to take effect.
Default value is still 90 days if not modified by admin.

The current @mention (for user names and channel names) uses the regex `\b` to detect the name boundaries, however that token doesn't support unicode characters. This solution replaces the word boundary with regex that match end of the word with any of the following white space, colon, comma and dot.

However, ending a name with a dot still has a problem as it doesn't get a mention link and this fix does not fix it. Part of the problem is that dots are allowed in the name validation regex. So this problem need to be solved later.

Another thing that this fix adds is a description to the UTF8 Name Validation settings, to inform chat admins about the characters that they need to avoid using in their regexes to not break other chat functionalities that depends on special characters to denote special meanings.

Most SMTP servers will only accept valid email address for sender. #766