Fix and update timezone default and doc

[michaelortmann]

Found by: https://github.com/thommey and https://github.com/dchmelik
Patch by: https://github.com/michaelortmann
Fixes: #461 and #1831

One-line summary:
Fix and update timezone default and doc

Additional description (if needed):

Test cases demonstrating functionality (if applicable):
Test 1
myeggdrop.conf:

#set timezone "America/New_York"
#set env(TZ) "$timezone"

Local time is now 02:53
Test 2
myeggdrop.conf:

set timezone "America/New_York"
set env(TZ) "$timezone"

Local time is now 20:55

[michaelortmann]

@thommey: This fix is similar to what you ask in issue #461, but not quite the very same. I aim to fix both Issues with this PR. $timezone is used in scripts. In the ones we ship by default:

eggdrop/scripts/ques5.tcl

Lines 366 to 367 in d317ac2

	if {![info exists timezone]} {
	set timezone [clock format 0 -format %Z]

I was thinking about switching the timezone and env settings in eggdrop.conf:
instead of:

#set timezone "Europe/Berlin"
#set env(TZ) "$timezone"

we could:

#set env(TZ) "Europe/Berlin"
# Set variable timezone for tcl scripts. This variable is deprecated and will be removed in a future release.
#set timezone $env(TZ)

But then i realized, if users only want to set the timezone variable and not the env(TZ) this make sthings more complicated for them.
So my new proposal is:

# Variable timezone for tcl scripts is deprecated and will be removed in a future release. So in a future release set env(TZ) "Europe/Berlin" directly instead.
#set timezone "Europe/Berlin"
#set env(TZ) "$timezone"

And when we later remove variable timezone, we patch ques5.tcl to use env(TZ) directly.
I hope someone comes up with a better doc wording here.