Update features.php

[ptitfrap]

In importing csv file features, clear query before making the new one for getting max ordering value.

[ilhooq]

Thank for your contribution. However, I didn't merged this pull request for this reasons :

• Although we can manually order features in backend, I deactivated this in frontend because, in practise, 90% of people want an alphabetical sorting. Indeed, it's a little bit confusing. I think that the correct implementation should be to let the administrator choose for each features list how it will be sorted.
• Property picture resizing should be done on the fly in fronted (look for current thumbnails implementation). This is more flexible if you want to change the size of all the pictures by deleting the cached thumbnails directories.
• Also, send one logical unit of change per pull request. Here, your pull request contains two logical units of change : features ordering and picture resizing.