category: introduce a microservice

[php-coder]

Here is the list of CategoryService methods that need to be ported/re-implemented:

Method	Used by	Outcome
add	CategoryController.processInput	Need an endpoint: yes
findIdsByNames	SeriesInfoExtractorServiceImpl.extract -> SeriesInfoExtractorServiceImpl.extractCategory	Need an endpoint: ?
findIdsWhenNameStartsWith	SeriesInfoExtractorServiceImpl.extract -> SeriesInfoExtractorServiceImpl.extractCategory	Need an endpoint: ?
findAllAsLinkEntities	CategoryController.showCategories	Need an endpoint: ?
findCategoriesWithParents	(SeriesController.showForm, SeriesController.processInput, SeriesImportController.showRequestAndImportSeriesForm, SeriesImportController.processImportSeriesForm) -> SeriesController.addCategoriesToModel	Need an endpoint: ?
findOneAsLinkEntity	CategoryLinkEntityDtoConverter.convert and @Category	Need an endpoint: ?
countAll	SiteController.showIndexPage	php-coder/mystamps-category#1
countCategoriesOf	CollectionController.showInfoBySlug	Need an endpoint: yes (in collection service)
countBySlug	UniqueCategorySlugValidator.isValid and @UniqueCategorySlug (used only in AddCategoryForm)	Need an endpoint: ?
countByName	UniqueCategoryNameValidator.isValid and @UniqueCategoryName (used only in AddCategoryForm)	Need an endpoint: ?
countByNameRu	UniqueCategoryNameValidator.isValid and @UniqueCategoryName (used only in AddCategoryForm)	Need an endpoint: ?
countAddedSince	CronServiceImpl.getDailyReport	Need an endpoint: ?
countUntranslatedNamesSince	CronServiceImpl.getDailyReport	Need an endpoint: ?
getStatisticsOf	CollectionController.showInfoBySlug	Need an endpoint: ?
suggestCategoryForUser	SuggestionController.suggestCategoryForUser	Need an endpoint: ?

Part of #1162

[php-coder]

The separate repo has been created: https://github.com/php-coder/mystamps-category