Add missing sentence segmentation in funding and acknowledgement

[lfoppiano]

This PR implement fixes the way the funding-acknowledgment parser handles an already formatted statement and preserve their existing elements (references, sentences). #1090

This PR fixes the following problems:

• sentence segmentation lost for funding and acknowlegment statements
• reference markers are lost after the funding-acknowlegment parser is applied

The initial solution proposed in the #1090 discussion, to re-apply a sentence segmentation that act on the transformed TEI structure was not applicable because it was not possible to re-generate the sentence coordinates as the TEI-XML elements do not have anymore layout-token information.

NOTE: this should be merged after #1096

[coveralls]

coverage: 40.787% (+0.6%) from 40.236%
when pulling bbca7dd on bugfix/sent-seg-ack-fund
into cb7118d on master.

[lfoppiano]

I did run all documents from PLOS, PMC and biorxiv over this, I've checked manually differences for a sample from each corpus. I also checked manually the merging of the coordinates for certain problematic documents that were causing problems in the past. It seems that everyhting looks good.