Move containsElementData to FlatLinearData next to isElementData. Move
tests for both methods to FlatLinearData.test.js.
Change-Id: I07a192f5925da7cc763efe5e41427f1f47d85850
Previously we returned ElementLinearData from the converter, then
stripped out the MetaLinearData. This meant that before processing
the ElementLinearData from the converter actually contained metadata
which is confusing.
The new document constructor stores the converter results in a
FlatLinearData object and simultaneously populates element and meta
data stores.
Also in this commit I have moved various methods from ElementLinearData
to FlatLinearData, from which ElementLinearData inherits.
Change-Id: I64561bde2c31d8f703c13ac7b0a0c5f7ade9f3d4