Add a Prebid label to console logs

[andyblackwell]

Type of change

• Bugfix
• Feature
• New bidder adapter
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Does this change affect user-facing APIs or examples documented on http://prebid.org?
• Other

Description of change

Prefix prebid console logs with a label. Easier to single out prebid logs at a glance, and makes it simple to filter down to just prebid logs.
notes:
- I removed the current param count limitations for a few of the methods (logMessage, logInfo, logWarn), so they can behave like the native methods
- because of this, I removed current formatting that injects the text : params : between the current params 1(msg) and 2(args ) output
- label color is Prebid blue #3b88c3, taken from prebid.org

Other information

[andyblackwell]

Looks like a false positive circleci failure:

1) should have unique slot name parameter
     Yieldbot Adapter Unit Tests buildRequests
     request is undefined
@webpack:///test/spec/modules/yieldbotBidAdapter_spec.js:945:6 <- test/test_index.js:138495:11

Doesn't seem like I have the ability to re-run the test, so will wait for some help there.
(Using this PR as my intro to contributing)

[jsnellbaker]

LGTM

[mkendall07]

very nice and clean. Thanks!