Added file wise coverage check

Checks every file if it is in the configured coverage range and throws a warning if this is not the case.

Extend configuration through:

        jasmine_node: {
            coverage: {
                thresholds: {
                    lines: 75,
                    statements: 75,
                    branches: 75,
                    functions: 90
                }
            }, ....
Merge pull request #4 from Nomeasmo/patch-1

Added file wise coverage check