Make result set an iterable

[pm47]

This allows us to use the full power of scala collections, to iterate
over results, convert to options, etc. while staying purely functional
and immutable.

There is a catch though: the iterator is lazy, it must be materialized
before the result set is closed, by converting the end result in a
collection or an option. In other words, database methods must never
return an Iterable or Iterator.

[codecov-commenter]

Codecov Report

Merging #1823 (6ed7c27) into master (98cae45) will decrease coverage by 0.04%.
The diff coverage is 93.54%.

@@            Coverage Diff             @@
##           master    #1823      +/-   ##
==========================================
- Coverage   89.39%   89.35%   -0.05%     
==========================================
  Files         145      145              
  Lines       11034    10973      -61     
  Branches      456      457       +1     
==========================================
- Hits         9864     9805      -59     
+ Misses       1170     1168       -2     

Impacted Files	Coverage Δ
...main/scala/fr/acinq/eclair/db/DbEventHandler.scala	93.54% <ø> (+3.22%)	⬆️
...n/scala/fr/acinq/eclair/db/FileBackupHandler.scala	71.42% <ø> (ø)
.../src/main/scala/fr/acinq/eclair/db/NetworkDb.scala	100.00% <ø> (ø)
...src/main/scala/fr/acinq/eclair/db/PaymentsDb.scala	92.85% <ø> (ø)
.../scala/fr/acinq/eclair/db/sqlite/SqliteUtils.scala	100.00% <ø> (ø)
...ain/scala/fr/acinq/eclair/db/pg/PgPaymentsDb.scala	84.81% <37.93%> (-0.51%)	⬇️
...main/scala/fr/acinq/eclair/db/jdbc/JdbcUtils.scala	96.07% <100.00%> (+0.16%)	⬆️
...c/main/scala/fr/acinq/eclair/db/pg/PgAuditDb.scala	98.23% <100.00%> (-0.04%)	⬇️
...ain/scala/fr/acinq/eclair/db/pg/PgChannelsDb.scala	96.29% <100.00%> (-0.05%)	⬇️
...main/scala/fr/acinq/eclair/db/pg/PgNetworkDb.scala	97.84% <100.00%> (-0.03%)	⬇️
... and 15 more

[t-bast]

It feels much more natural than the previous awkward manual handling!