Attribution page completed, altered logos

Attributions page: Added links to relevant trademarks; Improved styling
for better readability on mobile devices; Added disclaimer; Changed
icons to be the same as those actually used in the document; Corrected
text for some entities whose trademarks were not actually registered;
Homogenised TMs text; Moved entity names to be in alphabetical order

Index: Google Plus->Google+ as per trademark; History section now has
space for the relevant text; MD social icons are spaced 12 pixels apart

Replaced current g+ logo with trademark-compatible logo

Renamed DB2.svg to ibm.svg