Do not clear active line and active word markers

[hansbugge]

What's in this PR?

Changes the logic in handleMarkers to exclude the special markers for active line and selected word.

List the changes you made and your reasons for them.

• Added check that current marker does not have special class name ace_active-line or ace_selected-word before clearing it.
• Added new test to verify new behaviour.
• Changed test "should clear the markers" to reflect that not all markers should be cleared anymore.

References

Fixes

Fixes #190.

Progress on:

[coveralls]

Coverage increased (+0.2%) to 92.979% when pulling 018f1af on hansbugge:keep-active-line-marker into 8ed2dc0 on securingsincity:master.