Use GitLab CI instead of Circle CI

This also now only publishes the master snapshot of wikipedia.jar, now that pt_assistant is being built on Travis CI, the master snapshot of that plugin can be published there.
7 jobs for master in 8 minutes and 52 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #79438570
assemble

00:02:11

 
  Test
passed #79438571
build

00:03:12

passed #79438573
compile against latest JOSM

00:01:52

passed #79438572
compile against min JOSM

00:01:44

 
  Deploy
passed #79438575
publish master update site

00:01:36

passed #79441621
upload to transifex

00:01:51

failed #79438574
upload to transifex

00:04:15