Balance sounds, remove silent water footstep

[paramat]

Closes #2749

I created a sound testing area for my PR #2768 so i decided to make more use of it and check and balance all other MTG sounds.
Some new sounds were added recently and some of these needed a little adjustment.
All MTG sounds were tested for balance, any not appearing in this PR were therefore already balanced.

Many positional sounds were too loud because testing was not done at a close distance.
To balance positional sounds i moved the player as close as possible to the sound, then adjusted for a 'fairly loud but suitably and not uncomfortably loud' volume.

Changes:

• Many footsteps were too loud (as reported in a recent issue):
  Wood. Often complained about as a too-loud 'player is wearing clogs' sound.
  Dirt.
  Stone 'hard footstep'.
  Ice footstep.
  Metal footstep. The high volume made metal sound thin, hollow and 'tinny', not solid.
• Gravel footstep was actually too quiet =) Gravel is loud to walk on.
• 'default dig choppy' was slightly too loud. It was left undefined so fell back to its engine default gain of 0.5. Now it is defined in the wood sound defaults table as 0.4.
• 'default dig crumbly' was slightly too loud. It was left undefined so fell back to its engine default gain of 0.5. Now it is defined in the dirt sound defaults table as 0.4.
• Active furnace sound was too loud.
• Furnace item smelt was too loud.
• Torch 'on flood' was too loud.
• 'cool lava' was too loud.
• 'item smoke' had undefined gain, defaulting to 1.0, now it is specified as 1.0 for clarity.
• Flint and steel was too loud.
• 'gunpowder burning' was set at gain 2.0. Any value exceeding 1.0 results in a volume that to some extent does not reduce with distance. Now set to 1.0 and volume changes suitably with distance.
• 'tnt ignite' had undefined gain, defaulting to 1.0, now it is specified as 1.0 for clarity.
• Hoe on use was too loud, now balanced with 'default dig crumbly' (note: as this is a positional sound, the balance occurs at 0.3, not 0.4).
• The silent water footstep sound (4) is removed as it often causes swimming sounds to be excessively delayed when first entering the water. Also, excessively long silences can occur when 2 silent sounds are played in sequence.

[KaylebJay]

Nice work, I'll have to test this.

[paramat]

Simple and easy to review PR with a large benefit to very many users. Many sound levels are poorly balanced, and further balancing was also needed for the new sounds recently added. Therefore seems a fairly important PR.

I will probably not work further on this PR so if a core dev wants something changed to make it approvable feel free to make the change and then merge it.

[paramat]

1 year bump =D
This PR really should be merged, it is high priority fundamental maintenance.

The new footstep sounds were merged without their sounds being properly balanced, the intention was too balance the sounds in a follow up PR, which is this PR.
This PR also fixes some broken stuff related to sounds code, and fixes the silent water problem.
Apart from the above, all other sounds have been checked and were balanced if necessary, some were in a very bad state.

I was a core dev when i submitted this PR so i think my approval should still count, meaning only 1 extra approval is needed.
If no-one has time to review, just merge it long before a release and check the levels are ok as you subsequently use MTG, you can always adjust later if necessary. This is very good work and i could be trusted at the time i submitted this.

[sfan5]

Tested a few, sounds good.

[appgurueu]

Literally sounds well.