BHV-10114 Separate index bound updating part from updateMetric()

To update index bound, calling updateMetric() is too expensive.

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com
BHV-10114 Clear logic and add comments

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com
BHV-10114 Make protected logic against direct calling of `updateIndexBound`

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com
BHV-10114 fix logical fault

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com
BHV-10114 When model added or removed, index bound should be updated

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com
BHV-10114 Replace methods to right position

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com
Merge pull request #758 from enyojs/BHV-10114-davidum

Bhv 10114 Break down updateMetric() to increase performance

Looks good, thanks for all the updates!

Reviewed-by: Aaron Tam (aaron.tam@lge.com)