Pimcore cleaning for no error on E_ALL error_reporting level.

First commit "init" is after local installation, this one should not be merged with the main branch.

Purpose of the correction is to provide Pimcore free of error even on E_ALL level. Corrections have been made by viewing all the front web page from the demo_website, and all the menu, sub-menu, window, tab, etc., in the backend as much as possible.
If E_ALL is activated, Pimcore demo front and admin run now without any strict/notice warning! So great. I imagine there are some left, but it should be a good base.

Advantages of providing this:
- quality of the Pimcore application seen by the developpers. Having an application wich bootstrap without any strict/notice error means quality of the product.
- quality of futur plugins: E_ALL level can now be activated in the startup.php for developpers and they can have a working backend and develop their own plugin with this level. Actually this is not possible, bringing less quality code for the plugins or difficulty for developpers to achieve this.
- strategic feature provided by some competitor of Pimcore, so Pimcore has to improve on this field. One of them (PIM Akeneo) is proud to said their application has no strict error (see github they are chasing them) for exemple.
- the more important is this one: possibility to develop an application based on Pimcore with level E_ALL without having to add @ in many Pimcore method, slowing down developement, hidding  errors, ... Final application is stacked beetwen a clean developper work / Pimcore / Zend... Pimcore fill the logs... : ((

I started this because I try to make my developer team work in E_ALL level for quality of the code, but Pimcore has not this level of agrement and it is a shame as there is not so much things to change. It is a good basis, but I hope one day, for the long run, Pimcore would be unit tested/developped by core team in E_ALL level. Zend reporting zero notice/strict, and work transparent at this level, that is what we can call quality professional framework, and really Pimcore deserve to be able to work flawlessly too, it is a so good PIM/WCMS : )