Scalafix, scalafmt and minor cleanups

[jgogstad]

• Replace scalastyle with scalafmt
• Introduce scalafix
• Add scalafmt and scalafix checks to Travis build
• Use cats syntax instead of type class instance methods in SftpStore
  • Scalafix blew up on formatting this. It became a lot more readable with the syntax, especially the outer flatMaps.
• Minor stuff: Cleanup gitignore, add note to changelog that release notes goes to github release notes, move sshd_config from root directory to sftp/src/test/resources

[codecov]

Codecov Report

Merging #17 into master will increase coverage by 0.03%.
The diff coverage is 71.89%.

@@            Coverage Diff             @@
##           master      #17      +/-   ##
==========================================
+ Coverage    67.9%   67.93%   +0.03%     
==========================================
  Files           8        8              
  Lines         296      315      +19     
  Branches        8        8              
==========================================
+ Hits          201      214      +13     
- Misses         95      101       +6

Flag	Coverage Δ
#scala_2_12_10	67.93% <71.89%> (+0.03%)	⬆️
#scala_2_13_1	67.94% <72.18%> (+0.03%)	⬆️

Impacted Files	Coverage Δ
core/src/main/scala/blobstore/fs/FileStore.scala	97.14% <100%> (+0.08%)	⬆️
core/src/main/scala/blobstore/Path.scala	93.75% <100%> (+1.44%)	⬆️
core/src/main/scala/blobstore/package.scala	100% <100%> (ø)	⬆️
box/src/main/scala/blobstore/box/BoxStore.scala	5.06% <3.03%> (-0.2%)	⬇️
s3/src/main/scala/blobstore/s3/S3Store.scala	78.43% <76.19%> (-3.21%)	⬇️
sftp/src/main/scala/blobstore/sftp/SftpStore.scala	87.87% <90%> (+0.99%)	⬆️
gcs/src/main/scala/blobstore/gcs/GcsStore.scala	91.17% <93.75%> (-2.38%)	⬇️
core/src/main/scala/blobstore/StoreOps.scala	92.85% <95%> (+0.85%)	⬆️

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[jgogstad]

Addressed comments and some formatting mistakes, primarily from having multi-line blocks in parenthesis instead of curly brackets (see b61f9af..854f3ea).