Rename the binary files of curl-impersonate so that the Firefox and
Chrome versions can co-exist on the same system. The Firefox version is
now named 'curl-impersonate-ff' and 'libcurl-impersonate-ff' and the
Chrome version is named 'curl-impersonate-chrome' and
'libcurl-impersonate-chrome'. The wrapper scripts look for these names
as well. Symbolic names with the old names are still created inside the
Docker images to keep compatibility as much as possible.
In preparation for merging the support for Chrome impersonation, move
all build files to the 'firefox' folder. The two builds will live
separately as they are rather different (using two different SSL
libraries for instance).
