Create Section and SectionItem models

[apradillap]

Connects to #1013

What does this PR do?

Create two new models in GobiertoCMS module:

• Section: a section is a container of section items. Belongs to a site, and when destroyed, all its section items should be destroyed. Attributes:
• localized title
• site_id (references to Site)
• slug

SectionItem: a section item belongs to a Section. Attributes:

• item_id
• item_type
• position
• parent_id (references to SectionItem)
• section_id (references to the Section)
• level (it can be useful to render the tree)

How should this be manually tested?

From console show the section and section item

[codecov-io]

Codecov Report

Merging #1028 into master will increase coverage by 4.85%.
The diff coverage is 95%.

@@            Coverage Diff             @@
##           master    #1028      +/-   ##
==========================================
+ Coverage   78.59%   83.45%   +4.85%     
==========================================
  Files         414      413       -1     
  Lines       10654    10101     -553     
==========================================
+ Hits         8374     8430      +56     
+ Misses       2280     1671     -609

Impacted Files	Coverage Δ
app/models/gobierto_cms/section_item.rb	100% <100%> (ø)
app/models/site.rb	96.07% <100%> (+0.03%)	⬆️
app/models/gobierto_cms/section.rb	90.9% <90.9%> (ø)
.../controllers/gobierto_people/welcome_controller.rb	90.9% <0%> (-9.1%)	⬇️
app/mailers/application_mailer.rb	92.3% <0%> (-7.7%)	⬇️
app/controllers/gobierto_admin/base_controller.rb	89.74% <0%> (-7.7%)	⬇️
app/models/gobierto_budgets/budget_line_stats.rb	84.5% <0%> (-2.82%)	⬇️
...obierto_admin/gobierto_people/people_controller.rb	83.05% <0%> (-2.46%)	⬇️
app/models/gobierto_budgets/site_stats.rb	75% <0%> (-1.05%)	⬇️
app/models/gobierto_admin/permission.rb	100% <0%> (ø)	⬆️
... and 21 more

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[ferblape]

👍 Just fix the schema.rb and feel free to merge to master.

[ferblape]

careful

[ferblape]

careful