Allow pre-receive hook customization

This hook can be used for example to reject too large commits and it is
executed before "update" hook, used exclusively by Gogs to update its state.

https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks

Consistent tab indentation for all source files

This commit improves templates readability, since all of them use consistent
indent with all template command blocks indented too.

1. Indents both HTML containers such as <div>, <p> and Go HTML template blocks
   such as {{if}} {{with}}

2. Cleans all trailing white-space

3. Adds trailing last line-break to each file

This does not change any content and generated gogs.css is still the same.

Update Russian translation

Render commit msg as header + verbatim description

Most commit in Git are expected to follow standard of single header line,
followed by description paragraphs, separated by empty line from previous block.

Previously Gogs were treating everything as single header. Now we are trying to
render only first line as header, but following lines (description chunks) as a
verbatim.

Fix misspelled words

UI: Use more subtle grey SHA1 labels

With grey SHA1 labels, we should consider having also more subtle strips on
commits list. As current strips blend too much with grey SHA1 labels and top
bar, making hard to distinguish headers from content.

UI: Remove CSS rule making last-commit SHA bold

Current green SHA1 labels are more pronounced than other UI elements attracting
attention as if they were most important thing in the UI, while they are not as
important, especially without real Git client.

Using grey SHA1 labels makes the UI more balanced, less aggressive and lets
user to focus on other content elements.

NOTE: Neither GitHub or Bitbucket uses so heavy pronunciation as Gogs.

This removes remains from old design, that was not cleaned by previous #2068 PR.