Add @author rule in checkstyle

[htynkn]

According to code-conventions, "@ author" tag is not allow in source code.

I notice some PR and some test code still have "@ author" tag, considering we already have checkstyle plugin, I suggest add a new rule to check @ author tag. it can save time to review PR.

Some configuration sample:
https://github.com/danielb987/EmojicodeEditor/blob/master/checkstyle/emojicode_checks.xml#L93

[carryxyh]

Agree with this proposal.
I think:

1. We should check and remove present author tag.
2. The same thing should be done in branch 2.6.x.
   :)

[htynkn]

I notice the checkstyle is skip since 81c3c0d
so currently in travis ci, the checkstyle plugin is not running

[kimmking]

@htynkn
I think we should post this proposal to mail list.

[diecui1202]

@htynkn I suggest running checkstyle and rat plugin during release phase. For daily travis ci, just running mvn test, it needs to be completed ASAP.

Now the ci task takes a bit long time.

[markt-asf]

An approach I have seen taken in other projects is to remove @author tags but move the names to the appropriate POM section (if they are not already present).

[diecui1202]

I've enabled checkstyle and rat plugin for default travis CI.

[diecui1202]

#2393