add cell death and increased/decreased child terms

[sbello]

• increased cell death: Reduced vital functions inhering in several cells in a population or in significant parts of a tissue or organ
• decreased cell death: A slight reduction of vital functions inhering in cells of a population or some part of a tissue or organ
• cell death: The cessation of all vital functions inhering in a cellular population or cells in any body part such as tissue or organ

Motivation is that GO is obsoleting the terms cell death and necrotic cell death but for phenotypes we need this.

See discussions on the Phenotype editor's call minutes

GO cell death (GO:0008219) definition
Any biological process that results in permanent cessation of all vital functions of a cell. A cell should be considered dead when any one of the following molecular or morphological criteria is met: (1) the cell has lost the integrity of its plasma membrane; (2) the cell, including its nucleus, has undergone complete fragmentation into discrete bodies (frequently referred to as apoptotic bodies). The cell corpse (or its fragments) may be engulfed by an adjacent cell in vivo, but engulfment of whole cells should not be considered a strict criteria to define cell death as, under some circumstances, live engulfed cells can be released from phagosomes (see PMID:18045538).

Need to know from GO if cell death will stay as a do not annotate term in the long term. If it does then UPheno could continue to use this term
Related to geneontology/go-ontology#24680