Improve Image-ALT descriptions

[Zabuzard]

Most of our Image-ALT descriptions are rather cryptic and heavy abbreviations.

Examples:

![MCRst](../../../img/pilot_master_caution_reset.jpg)
![FrontTCN](../../../img/pilot_tacan.jpg)
![wso_oxygen_regulator_panel](../../img/wso_oxygen_regulator.jpg)

While better than nothing, they should still be improved to create a better experience in the following cases:

• Website integrated search (which displays the names in the preview)
• External search tools (better search results)
• Deactivated images during Data Roaming (mobile users)
• Users of screen-readers (impaired eyesight etc)