Use maven plugin as default code style checker for project

Currently, [Inspections] Core suite [1] on TC doesn't work well enough. The suite has a FAILED status for more than 2 months due to some issues on TeamCity application [2]. It confuses most of the members of the Apache Ignite community.

Moreover, this suite is no longer checks configured rules. For instance, in the master branch, 11 Unused imports can be found (e.g. for {{IgniteCachePutAllRestartTest}
[3]).

I think the maven-checkstyle-plugin should be used as the default code style checker.
Advantages:

• An IDE agnostic way for code checks
• Can be used with different CI and build tools
• Executable from the command line
• Single configuration

[1] https://ci.ignite.apache.org/viewType.html?buildTypeId=IgniteTests24Java8_InspectionsCore&branch_IgniteTests24Java8=%3Cdefault%3E&tab=buildTypeStatusDiv
[2] https://youtrack.jetbrains.com/issue/TW-58504
[3] https://github.com/apache/ignite/blob/master/modules/core/src/test/java/org/apache/ignite/internal/processors/cache/IgniteCachePutAllRestartTest.java#L29