TODO: Update old items and add a couple of new ones

This removes items already addressed, adds a couple of new ones, and
refines a couple of already existing items.
color.h: Rename header inclusion guard
user.h: Refine Doxygen comment blocks for various entities
usermodes.c: SetOnOffTimeState_handleIr(): Use logic for useAutoOffAnimation

The method beforehand was kind of a hack and is not required to work
under all circumstances. This makes sure a valid logical expression is
getting used.
usermodes.c: Simplify assignments of g_animPreview

As both values are boolean the value can be assigned directly without the need
for another if condition.
README: Refine some statements and add a section about contributions
user: Refine Doxygen comment block of various entities
user: Rename various entities

This renames UI_AUTOOFFTIMES_COUNT to UI_ONOFFTIMES_COUNT and
UserEepromParams::autoOffTimes to UserEepromParams::onOffTimes, which is
more consequent with the naming of the functionality itself.
usermodes.c: Rename NormalState::colorToSet to NormalState::propertyToSet
usermodes.c: Fix a typo within Doxygen comment block of NormalState::curHue
user.c: Fix coding style guideline violation
usermodes.c: Fix coding style guideline violation
usermodes.c: Introduce data type for properties to set within "normal" mode

This introduces the data type "propToSet" and applies it accordingtly to
distinguish between the properties that can be set within "normal" mode.
TODO: Update and/or remove items
usermodes.c: Move return into if condition

This change makes it more clear what is actually being returned, which
is false whenever the received command is not up and/or down.
usermodes.c: Enter "hue fading" mode AutoHueState_enter() correctly

This makes sure that the "hue fading" mode is entered correctly by removing
the call of the "ISR", which will be executed by the appropriate dispatcher
anyway. It sets up the counter with the proper value instead. Furthermore
the logic of the counter is inverted, so it is actually counting upwards,
which is more intuitive to understand.
usermodes.c: AutoHueState_enter(): Reset current hue

Beforehand the current hue was not explicitly set, which would result in a
different color each time the mode was entered. This makes sure the current
hue will get reset whenever the "hue fading" mode is entered, so it will
always start off with the same color.
Move COLOR_HUE_MANUAL_STEPS from color.h to usermodes.c and rename it

This moves COLOR_HUE_MANUAL_STEPS from color.h to USER_HUE_CHANGE_MANUAL_STEPS
in usermodes.c, as it makes actually more sense to place it there.
user.c: Get rid of variable not needed

Return the result directly, which makes the result variable useless.
Furthermore the function can now return directly instead of iterating
over each time.