pmd.xml: exclude TooManyStaticImports rule.

No functional changes.
SeriesInfoDto: fix PMD warnings about SingularField by another way.

Correction for 294d8a1799c9e14302d7cb3ddbe1150c47164620 commit were I fixed all SingularField
warnings but introduced another one: AvoidDuplicateLiterals.

No functional changes.
SeriesService{,Impl}: fixed PMD warnings about TooManyMethods by ignore these warnings.

No functional changes.