Make Git use LF newlines in *.java, *.properties (#765)

* Make Git use LF newlines in *.java

In .gitattributes, set crlf=input for *.java, so that:

* "git checkout" does not convert newlines, so they remain LF,
  even if the system Git configuration on Windows specifies
  core.autocrlf=true.
* "git add" converts CRLF to LF.

This is intended to fix the numerous checkstyle errors about CRLF
newlines that ci.jenkins.io reports when it builds the plugin on
Windows.

* Make Git use LF newlines in *.properties

ci.jenkins.io reported checkstyle CRLF errors for *.properties, too.

Author: KalleOlaviNiemitalo

.gitattributes

@@ -0,0 +1,2 @@
+*.java crlf=input
+*.properties crlf=input