insert messageEvolve into correct locations, replacing incorrect messageAlreadyMount

Currently, when you feed a pet enough to turn it into a mount, you see the messageAlreadyMount notification ("You already have that mount. Try feeding another pet."). This fix changes it to the messageEvolve notification ("You have tamed <%= egg %>, let's go for a ride!").
fix bug where an un-checked to-do with checklist removes only part of reward

When a to-do is checked off, the rewards are increased by the number of checklist items that have been completed. However as reported in https://github.com/HabitRPG/habitrpg/issues/3474, if the to-do is later un-checked, then the rewards subtracted are not being similarly increased by the number of checklist items completed. This fix will change that - the number of checklist items completed will have an equal effect on checking and unchecking a to-do.

This of course won't fix the problem of, upon unchecking, not being able to calculate the exact value of the rewards that had been given upon checking, so there will still be a discrepancy between checking and unchecking, but it will be much smaller than it is currently.
add correct message for equipping equipment

Currently, when you put on equipment, you see the messageBought notification. There was no messageEquipped notification in the code so I've added one.

I've updated ALL locale files IN ENGLISH, following the convention already in place for using English when there is no translation (e.g., locales/pl/messages.json, locales/sv/messages.json).
Merge pull request #219 from Alys/messageEquipped

add correct message for equipping equipment
Merge pull request #218 from Alys/todo-with-checklist-untick

fix bug where an un-checked to-do with checklist removes only part of reward
Merge pull request #217 from Alys/messageEvolve

insert messageEvolve into correct locations, replacing incorrect messageAlreadyMount
chore(i18n): update locales
fix(i18n): another possible hotfix for wrong language, @lefnire this one works on my local computer but maybe it will not work on prod like the other one
feat(drops): Tweak contrib bonuses

At @deilann's request, divide the drop chance bonus for contributor levels in half and add a +1/level contributor bonus (subject to the subscription multiplier once implemented in private code) to drop cap.
fix(text): The Potion that gives Health...

...is a Health Potion.
chore(i18n): update locales
fix(i18n): update broken code inside translations
chore(grunt): grunt
feat(mystery): 0 GP mystery items @deilann
fix #3513 - if contrib level is NaN, use 0

Fixes (I hope) https://github.com/HabitRPG/habitrpg/issues/3513. NOTE that private code will need to be edited too - ref https://github.com/HabitRPG/habitrpg-shared/commit/f49ed5436c60d6b135909a3c8714347d99499701
Merge pull request #221 from Alys/fix

fix #3513 - if contrib level is NaN, use 0
fix(accessories): add body accessory to user model, fixes https://github.com/HabitRPG/habitrpg/issues/3346
feat(mystery): add 05/2014 mystery item
chore(i18n): update locales
show "unequipped" message instead of "equipped" when taking off gear