Updates to various FortiProducts (ref #858) and check.py fixes

[eantowne]

Before submitting a pull request, please check the following.

---

When updating an existing appliance:

• [X] The new version is on top.
• [X] The filenames in the "images" section are unique, to avoid appliances / version overwriting each other.

• [X] If you forked the repo, running check.py doesn't drop any errors for the updated file.

  fortianalyzer.gns3a & fortimanager.gns3a:

• 6.4.14
• 7.0.11
• 7.4.2

fortigate.gns3a:

• 6.4.15
• 7.0.14
• 7.2.7
• 7.4.3

Changed appliance version 5->4 for 3 different mikrotik appliances that were throwing warnings from check.py.