Different keyboard layouts

## Expected Behavior
Zoom in shortcut Ctrl+= is not standard and breaks the workflow in spanish.

Typical zoom shorcuts are:
- Ctrl++: Zoom in
- Ctrl+-: Zoom out
- Ctrl+0: Reset zoom

I check other programs (tilix https://github.com/gnunn1/tilix/blob/master/data/gsettings/com.gexperts.Tilix.gschema.xml#L1191) and this is pretty standard.

In spanish Ctrl++ is a direct key press. To use Ctrl+=, we need to press Ctrl+Shift+0.

Seems in english is the opposite and Ctrl++ is not a direct keypress.

## Current Behavior

Ctrl+= executes zoom in.

## Possible Solution

- Stick to standards.
- Deal with this in a `l10n` way
- Allow to customize shortcuts

## Context
- Akira Version: master
- OS Info: Arch linux