Norwegian language added

Started translating into Norwegian
Norwegian language update
Norwegian language update
Norwegian language update
Norwegian language update
Added Norske Kroner
Norwegian language update
Norwegian language updated.

All language files now translated into Norwegian. Keep in mind that this
is the first complete translation and it may be some discrepancies.
Norwegian language update.

Fixed some format issues.
Merge pull request #156 from sandbugt/master

Norwegian language translation.
Seeding ok with MySQL STRICT_TRANS_TABLE, fixes #157
Migrations for accounts and users tables

Now when clicking on INVOICE NOW, we can reach first step of a new
invoice creation even with MySQL 5.6 default STRICT_TRANS_TABLE.
Client import, create invoice with STRICT_TRANS_TABLE
nullable added to some fields
default integer value for payment_terms

Because sending an empty string to a integer column is not allowed with
MySQL in STRICT_TRANS_TABLE mode.
simpler short conditionnal

“Since PHP 5.3, it is possible to leave out the middle part of the
ternary operator. Expression expr1 ?: expr3 returns expr1 if expr1
evaluates to TRUE, and expr3 otherwise.”
http://php.net/manual/en/language.operators.comparison.php
3 constants taken from config
Hardcoded urls removed in mail templates
Tracking activity when invoice is archived
Merging chages