Switch to clang-format

[antoinealb]

I added support for clang-format and ran it on the whole source tree. Uncrustify that we have been using so far is slowly dying, its output is unstable from version to version and it has less capabilities than clang-format. I tried not to change too much the code, but due to our inconsistent formatting, some changes were needed anyway.

Reasons for doing this:

• Propper formatting of code, including macros and protobuf files
• Stable output
• C++11 compatibility
• Easier to configure

Reasons for not doing this:

• Git blame will be broken for a while. This can be mitigated by looking at a file history directly.
• Pull requests currently in-flight will probably be broken (sorry)

Note that this was tested on an install of Clang 7, make sure you have a recent enough version!

[SyrianSpock]

Please wait for #175 to be merged before merging this.

[antoinealb]

Rebase now that #175 landed. Pinging @SyrianSpock for review 👍