Fix: Unable to set spell group to 'NONE'

[Tofame]

Pull Request Prelude

• [x ] I have followed proper The Forgotten Server code styling.
• [x ] I have read and understood the contribution guidelines before making this PR.
• [x ] I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

Using the spellgroup("none"), didn't work as below in the code, after it was already loaded, the code: if (group == SPELLGROUP_NONE) {, would have overriden it and set none to either attack or healing group.

This successfully fixes it.

If group is none, then we don't want to load/change group cooldowns, as other checks in the code for spell cooldown check only groupCooldown > 0, and not group != SPELLGROUP_NONE, so I think it will be more efficient to block it at loading.

Issues addressed:
'none' spell tag not working.
How to test:
Try to set spell's group to none, you will see using the spell will still put cd on attacking/healing group as this is what none is set to currently.

[Tofame]

Need to consider that initialization of variable groupCooldown is 1000, which is not supported by ifs related to applying/checking cooldown.
Need to further consider revscripts, as I changed XML parsing, but apparently revscript loading would need changes too.

[Tofame]

Okay so as @ArturKnopik said when I asked him on discord, he told me every spell has a group

So I've read more into that and currently he is right. There are 2 options that I think are viable:

1. Removing any code that takes parameters 'none'/'0' regarding to group in XML parser as its misleading, and not do anything more, leave SPELLGROUP_NONE as serving as 'undefined' group, then we assume that every spell is forced to have some kind of group. [This is how it works in TFS now]
2. Allow for spells to actually not have groups, so they can only have their own cd and not impose cooldowns on groups. This would require changes that I already submitted and a little change in revscript spell group loading. [This is what I suggest]

What do you think?

[Tofame]

Updated commit to adapt revscript loading, showing how it could look.

I dont like how I had to add new enum, especially with value 255, but Im pretty restricted as I must have in mind to keep everything compatible.