tools/qa-checks: Add header_check module

This patch adds the header_check module that checks the following :
- There is a header in all files given as arguments (except the ones
specifically ignored).
- The header years in all of those files are logical coherent with the last
file modification.

Issue-Id: SCM-2638
Signed-off-by: Hugo L'Hostis <hugo.lhostis@arm.com>
Change-Id: I22036a3de88693afde5992843dbf94f2c46cb4b4