/series/{id}: show similar series

[php-coder]

Some series from database are similar. For example, in many cases they are differ by perforation. Compare the following:

• https://my-stamps.ru/series/151
• https://my-stamps.ru/series/152
  Need a way to show similar series to user.

In order to complete this feature, we need to have the following:

• Similar series: create a table #968: a table for storing similar series
• Similar series: update view to show similar series #970: a view that shows similar series (guarded by togglz feature)
• service and dao for fetching similar series

[0pdd]

@php-coder 2 puzzles #992, #993 are still not solved.