Improve linemod2d clustering

[RunqiuBao]

In linemod2D,

1. use highest-score candidate first in linemod2D clustering, instead of merging everything inside cluster.
2. add critical direction in linemod2D clustering.

[jerasman]

@RunqiuBao typo "perpendiculr". Also, where are your new variables documented? I didn't see their description

[RunqiuBao]

Added docs and cleaned rotationalClustering.

[RunqiuBao]

notes:
(1) definition of long object by 5 is ambiguous.
(2) critical direction <- use a better name.
(3) should support thin plane object as well.

[RunqiuBao]

@jerasman
Updated:
(0) longAndNarrowThreshold can be configured as a parameter when rendering template.
(1) change criticalDirection to narrowDirection
(2) support both long object and thin plane object.