[PLAYER-42] customize toolbar order

[jparez]

Description

This PR adds the feature for ordered icons in the toolbar and displays separators.

A new option (toolbarOrder), which is an array, has been added to the options passed to the constructor of the player.
The IDs to include in the array correspond to the constructor name registered in the plugin.

static get name() {
    return 'StreamResolution';
}

For ButtonsEvents, the name is formed like this: ButtonsEvents_XXX, where XXX can be one of the following:
ROTATE, VOLUME_DOWN, VOLUME_UP, HOMEPAGE, BACK, or POWER.

These 3 commits are independent of this story:

• fix css on Battery
• clean code remaining in fullscreen plugin + delete remaining battery icon
• replace store mock in unit test by the real store

[pgivel]

A few questions but honestly this looks great. It adds a feature while making everything look cleaner in the code, I love it.

[caarmen]

Just reviewed the README :)

[caarmen]

Just checked out the README. Looks good!