Move tracing code to trace package

[krnowak]

This PR is a first part of N to resolve issue #1303.

Other than rather mechanical work of moving files to a subpackage and changing the used package name for the moved types in other packages from otel to trace it also does the following:

• Moved tracing parts of config.go to trace.
• Duplicated InstrumentationOption and WithInstrumentationVersion in trace (see trace/config.go).
• Added nolint:golint for trace.TraceID and trace.TraceIDFromHex (in `trace/trace.go).

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Krzesimir Nowak (5c117d4)

[codecov]

Codecov Report

Merging #1307 into master will increase coverage by 0.0%.
The diff coverage is 81.5%.

@@          Coverage Diff           @@
##           master   #1307   +/-   ##
======================================
  Coverage    77.2%   77.2%           
======================================
  Files         121     122    +1     
  Lines        5954    5955    +1     
======================================
+ Hits         4600    4601    +1     
  Misses       1111    1111           
  Partials      243     243           

Impacted Files	Coverage Δ
bridge/opentracing/util.go	100.0% <ø> (ø)
config.go	80.0% <ø> (-13.1%)	⬇️
exporters/stdout/exporter.go	25.9% <ø> (ø)
global/internal/state.go	100.0% <ø> (ø)
global/internal/trace.go	88.8% <ø> (ø)
global/trace.go	66.6% <ø> (ø)
internal/trace/parent/parent.go	0.0% <0.0%> (ø)
sdk/trace/sampling.go	100.0% <ø> (ø)
trace/trace.go	80.0% <ø> (ø)
trace/trace_noop.go	57.1% <ø> (ø)
... and 19 more

[MrAlias]

@krnowak can we update this line of the CHANGELOG to correctly describe where things were moved and include this PR in addition?

[krnowak]

Changelog updated, docs are still a TODO, but I suppose I could do them later, when the all the code is in its final place.

[krnowak]

Rebased.