Support content_type when downloading

[MFSY]

• Support downloading data of a given content-type
• When downloading, set the default json property path to follow to "distribution.contentUrl" in order to get the downloadable file urls and the default download path to the current folder
• Disable rewriting following SPARQL keywords: "as", "not", "exists", "group", "by"
• Updated SPARQL query statement builder to consider @id and @type values as URIs when used with the NOT_EQUAL operator
• Added methods to check if a Resource has an identifier or a type and added methods to get them

Fixes #251

[codecov-commenter]

Codecov Report

Merging #265 (f076e78) into master (9a04477) will decrease coverage by 0.31%. The diff coverage is 22.22%.

@@            Coverage Diff             @@
##           master     #265      +/-   ##
==========================================
- Coverage   72.57%   72.25%   -0.32%     
==========================================
  Files          86       86              
  Lines        5341     5374      +33     
==========================================
+ Hits         3876     3883       +7     
- Misses       1465     1491      +26     

Impacted Files	Coverage Δ
kgforge/core/archetypes/store.py	62.24% <0.00%> (ø)
kgforge/core/forge.py	70.05% <0.00%> (ø)
kgforge/specializations/stores/bluebrain_nexus.py	27.57% <20.00%> (-0.14%)	:arrow_down:
kgforge/core/resource.py	71.59% <21.73%> (-17.81%)	:arrow_down:
kgforge/core/commons/dictionaries.py	72.72% <40.00%> (-27.28%)	:arrow_down:
kgforge/specializations/resources/datasets.py	67.41% <50.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[crisely09]

Looks good to me.