linter: Improve i18n related regexes.
linter: Improve i18n related regexes.

There are four regexes which try to ensure that the i18n strings are
properly captured.

1) The one which disallows multiline strings.
```
i18n\.t\([^)]+[^,\{\)]$

// Disallows:
i18n.t('some '
       + 'text');
```

2) The one which disallows concatenation within argument to i18n.t():
```
i18n\.t\([\'\"].+?[\'\"]\s*\+

// Disallows:
i18n.t("some " + "text");
```

3) There are two which disallow concatenation with i18n.t():
```
i18n\.t\(.+\).*\+

// Disallows:
i18n.t('some text') +

\+.*i18n\.t\(.+\)

// Disallows:
+ i18n.t('some text')
```

The ideal case is that you try to bring the string argument to the
i18n.t() on one line. In case this is not possible, you can do the
following:

```
var1 = i18n.t("Some text to be translated");
var2 = i18n.t("Some more text to be translated");
complete = var1 + var2;

rht/zulip,kou/zulip,showell/zulip,synicalsyntax/zulip,eeshangarg/zulip,zulip/zulip,dhcrzf/zulip,punchagan/zulip,Galexrt/zulip,rishig/zulip,Galexrt/zulip,Galexrt/zulip,timabbott/zulip,brainwane/zulip,andersk/zulip,shubhamdhama/zulip,dhcrzf/zulip,hackerkid/zulip,tommyip/zulip,kou/zulip,kou/zulip,amanharitsh123/zulip,rishig/zulip,hackerkid/zulip,andersk/zulip,zulip/zulip,hackerkid/zulip,synicalsyntax/zulip,zulip/zulip,brockwhittaker/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,verma-varsha/zulip,tommyip/zulip,andersk/zulip,timabbott/zulip,showell/zulip,verma-varsha/zulip,showell/zulip,showell/zulip,brainwane/zulip,tommyip/zulip,brainwane/zulip,jackrzhang/zulip,kou/zulip,rishig/zulip,andersk/zulip,shubhamdhama/zulip,amanharitsh123/zulip,verma-varsha/zulip,eeshangarg/zulip,brockwhittaker/zulip,verma-varsha/zulip,synicalsyntax/zulip,punchagan/zulip,mahim97/zulip,jackrzhang/zulip,verma-varsha/zulip,mahim97/zulip,synicalsyntax/zulip,timabbott/zulip,Galexrt/zulip,punchagan/zulip,rht/zulip,Galexrt/zulip,hackerkid/zulip,verma-varsha/zulip,tommyip/zulip,synicalsyntax/zulip,showell/zulip,timabbott/zulip,hackerkid/zulip,mahim97/zulip,kou/zulip,jackrzhang/zulip,rht/zulip,eeshangarg/zulip,rishig/zulip,hackerkid/zulip,jackrzhang/zulip,dhcrzf/zulip,brainwane/zulip,shubhamdhama/zulip,dhcrzf/zulip,showell/zulip,andersk/zulip,Galexrt/zulip,brainwane/zulip,mahim97/zulip,kou/zulip,dhcrzf/zulip,zulip/zulip,mahim97/zulip,timabbott/zulip,rht/zulip,rishig/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,dhcrzf/zulip,rishig/zulip,tommyip/zulip,amanharitsh123/zulip,Galexrt/zulip,brainwane/zulip,timabbott/zulip,kou/zulip,rishig/zulip,rht/zulip,brockwhittaker/zulip,amanharitsh123/zulip,zulip/zulip,synicalsyntax/zulip,andersk/zulip,punchagan/zulip,mahim97/zulip,brockwhittaker/zulip,dhcrzf/zulip,andersk/zulip,amanharitsh123/zulip,eeshangarg/zulip,brainwane/zulip,shubhamdhama/zulip,tommyip/zulip,jackrzhang/zulip,eeshangarg/zulip,timabbott/zulip,punchagan/zulip,synicalsyntax/zulip,shubhamdhama/zulip,amanharitsh123/zulip,jackrzhang/zulip,shubhamdhama/zulip,tommyip/zulip,punchagan/zulip,hackerkid/zulip,shubhamdhama/zulip,brockwhittaker/zulip,rht/zulip,jackrzhang/zulip,brockwhittaker/zulip