Follow sound naming spec

The files in this theme should be renamed following the freedesktop sound naming spec.

Early mapping between the current sound names, Oxygen sounds, and the spec:

New:

Plug_device - device-added

Unplug_device - device-removed

Power_plug - power-plug

Power_unplug - power-unplug

Volume_change - audio-volume-change

Low_battery - battery-caution

Critical_battery - battery-low

SMS_notification - message-new

Generic_beep - bell-window-system

completion-partial

Trash - trash-empty

Sounds with Oxygen counterparts:

Original Blue Ocean name - Oxygen - Spec

Error - Oxygen-Sys-App-Error - dialog-error

Error_serious - Oxygen-Sys-App-Error-Serious - dialog-error-serious (not in spec but it allows naming more specific sounds)

Information_dialog - Oxygen-Sys-App-Message - dialog-information

Question-warning_dialog - Oxygen-Sys-Question - dialog-question

Generic_positive - Oxygen-Sys-App-Positive - outcome-success

Generic_negative - Oxygen-Sys-App-negative - outcome-failure

dialog-warning - Oxygen-Sys-Warning - dialog-warning

Log_out - Oxygen-Sys-Log-Out - desktop-logout

Log_out_short - Oxygen-Sys-Log-Out - service-logout

? - Oxygen-Im-Phone-Ring - phone-incoming-call

? - Oxygen-Sys-List-Match-No - completion-fail

? - Oxygen-Sys-List-End - completion-rotation

? - Oxygen-Sys-List-Match-Multiple - completion-success

Issues:

Plasma uses Oxygen-Sys-App-Positive and Oxygen-Sys-App-Negative in many places for positive and negative actions. There's no equivalent to that on the spec. What do we do? - Solution: Name them outcome-success and outcome-failure
There's no equivalent to SMS_notification on the spec, maybe we could rename it as 'message-new-sms', which is similar to 'message-new-email' but is not present explicitly on the spec? - Solution: rename to more generic 'message-new'.
Oxygen has Oxygen-Sys-Special. The only place where it's listed is under Accessibility notifications (SySe>Notifications>Application-specific settings> Accessibility), but the sounds are disabled by default. I checked all repositories under #6 but only KAccess uses them. Do we need a replacement for it or do we use another sound for that instead (e.g. beep sound)? - Solution: Replace it with the system bell sound.

@mart @ngraham (please tag more people that might be interested if you know any)