new top level .gitignore

[gyorb]

resolves #125

[gyorb]

@vodorok did we require build.log and bin directory in the gitignore file?

[vodorok]

I had a bin directory under ./eclipse-plugin/eclipse/cc.codechecker.eclipse.plugin. I think this folder is created by eclipse plugin m2e. By my understanding, this plugin is needed for building the plugin through eclipse. During the uplift development, I've needed to update the maven project multiple times with m2e, and this could created this bin directory. Please take a look on this related StackOverflow Answer. When I deleted the folder, and built the plugin, the folder wouldn't reappear, nor when checked out freshly and built on terminal. The build went fine, so I don't think this line is needed in the gitignores.
For the build.log: In my uplift work dir, I didn`t found this file generated.