Implement minimal Attack and UseSkill CombatAction

Added CHANGELOG.md by following git commits.

Reduces a lot of the object designs to be reusable resources that act as templates for factory methods.

* Update the readme, write about characters and a little bit about combat

Part 2 of #13

* first mockup for grid movement

* back to defaul enviroment

* Get the right information when creating the battle scene from the localmap scene

* first mockup for grid movement

* back to defaul enviroment

* Get the right information when creating the battle scene from the localmap scene

* substitute Game scene with the one with local map

* add local map and transition from it to combat

* cleanup incongruences between versions

* Add localmap to the scene

* bugfix for wrong indentation in Battler.gd . Avoid continously transition to combat if the player keeps the direction button towards the enemy (in the map)

* Deleted template comments; Class, script and filename renamed in CamelCase;
Signal in LocalMap connected in parent node.

Mana bars added

The bars system has been refactored. It's now possible to easily extend
it to create different bars i.e. stamina, rage, energy, etc..
The interface anchor has been removed and replaced with a proper control
node to hold the bars. Folder structure has also been cleaned.

Note that the newly added manabar will not show as of now since the
characters do not have mana at level 1 (not sure why). They were
configured to only appear if the battler has more than 0 of max mana.

Closes #31

Add Character Growth

Characters gain experience points at the end of battle, which contribute to their level.  Levels determine stat growth along defined curves for each character.

Skills system added

It's now possible to add skills as resources and use them in combat.
Some changes:

- Initial stats now have mana
- A combat action for skills has been added
- A really simple menu to select which action to perform in the given
turn
- Resource for skills
- Skills can be executed on a given chance

What can be improved:
- As of now, the skills have a `base_damage` which is added on top of the
already calculated damage in the `Hit` script. We might want to use the
strength as a multiplier to increase the overall damage of the skill,
for instance, instead of just adding them together.

- The menu for selecting the action is really simple and the UX is bad
to say the least. I'll create a separate issue for this.

- Skills are only available as a form of attack, i.e. you can't create
healing skill with the current system. But it can be extended to do so.

- They are not specific to jobs. For instance, both Dan and Blue are
fighters, but you'll have to add skills to them separately. Though, this
is most due to how they were created. We should probably create a
separate FighterJob and add the skills to them, this would fix the
problem imo.

Closes #16 and #15

Part 2 of #13

Prototype monster AI, choose target based on health

Renaming the job node in the editor on child scenes doesn't work, we'll need another solution like drawing in the viewport

closes #8

Closes #9

closes #11