[Patch] Documentation and migration to java 8 of preset code.

[michael2402]

While going through the preset code I documented some methods to save others the work to figure out what they mean.

I also migrated some parts of the code to java 8 (use lambdas, new predicates, stream.filter().findFist(), ...)

[stoecker]

Small Notes:

• TaggingPreset: "The icon name that was used for this preset." -> "assigned to" instead of "was used", that's used by the XML parser.
• For KeyedItem "Usage information on a" - a what?

[Don-vip]

In 10590/josm:

see #11390, fix #13191 - Documentation and migration to java 8 of preset code (patch by michael2402) - gsoc-core

[Don-vip]

In 10591/josm:

see #13191 - fix typos - gsoc-core

[michael2402]

Replying to stoecker:

Small Notes:

• TaggingPreset: "The icon name that was used for this preset." -> "assigned to" instead of "was used", that's used by the XML parser.
• For KeyedItem "Usage information on a" - a what?

Thanks for clarifying/fixing that.