migrate DPD to new roulier and python 3

[DylannCordel]

dpd has been renamed to dpd_fr_soap because this webservice is specific to France (and _soap as discussed in #138 and #140). I also have a dpd_sk_rest available if someone is interrested but I don't have any credentials to test it (it seems each country have it's own webservice)

[DylannCordel]

@florian-dacosta PR is ready to be reviewed. If you want to run tests, you need to ask to DPD France they allow your IP to access their test server.

[florian-dacosta]

Thanks for your work again.
For you information, DPD should change its webservice. It was planned for 2019 though, but they were not ready, but they still should do it sooner or later.
Here is the work that was done to meet their new webservice : https://github.com/akretion/roulier/tree/feat/dpd_2019
Not used yet, just so you know. We will probably need to switch when they will be ready.

[DylannCordel]

@florian-dacosta code rebased and dpd_fr renamed to dpd_fr_soap (as discussed in #138 and #140)

[florian-dacosta]

@DylannCordel
I didnt notice the PR was not up to date with master.
Merging it did break it because the last refactore here : ba5640c#diff-e2b8c9f0fa9c6966e5cb30dd546c57d799f60206afda0c7e15c85b915020bc8aR15

I made a fix, so all should be ok. But please, be careful if you update roulier and switch back to master for DPD, you should first confirm all is working properly.

[DylannCordel]

@florian-dacosta LGFM : tests are running from an allowed IP. We may ask to DPD to allow travis IPs for the test account or create a specific test account for roulier ?