Add variables for groups; add yell channel; add multi-channel support

[veev-code]

This PR adds significant new functionality to AutoFlood, greatly enhancing its capabilities for group recruitment and trade advertising:

Group Composition Variables

• Added support for {size}, {tanks}, {heals}, and {dps} placeholders to show current group composition
• Variable substitution only occurs when these placeholders are present in messages
• Group role detection uses the WoW API UnitGroupRolesAssigned for accurate counting

Math Operations for Role Variables

• Added support for math operations in placeholders: {4-tanks}, {5-heals}, {20-dps}
• Useful for showing how many more of each role you need (e.g., "Need {2-tanks} more tanks")
• Results never go below 0 for clean output

Special Need Format

• Added special format {need-2/4/14} that automatically formats needed roles with proper pluralization
• Format specifies target counts for tanks/healers/DPS, displaying only roles still needed
• Example: With 1/3/10 in group, {need-2/4/14} shows "Need 1 tank, 1 heal, 4 DPS!"
• Empty result when all roles are filled

Additional Channel Support

• Added support for yell channel (/y or /yell)
• Added support for direct channel numbers (e.g., /floodchan 2 for Trade channel)
• Fixed channel handling to properly identify all channel types

Multi-Channel Broadcasting

• Added support for broadcasting to multiple channels with different intervals
• Use comma-separated lists: /floodchan say,yell,guild and /floodrate 60,120,300
• If fewer rates than channels are specified, the last rate is reused for remaining channels
• If more rates than channels are specified, extra rates are ignored

Additional Improvements

• Immediate broadcast when enabling flood for instant feedback
• Improved information display for better readability
• Added new localizations in both English and French

This PR makes AutoFlood much more versatile for group leaders, raid organizers, and trade advertisers by providing dynamic content that updates based on actual group composition.

Closes:
#12
#8
#5